@article{hassan_2022, title={On 'Intracellular production of superoxide radical and of hydrogen peroxide by redox active compounds' by H. Moustafa Hassan, Irwin Fridovich}, url={https://doi.org/10.1016/j.abb.2022.109256}, DOI={10.1016/j.abb.2022.109256}, abstractNote={This commentary discusses how the idea of employing redox cycling compounds to generate partially reduced oxygen species (O 2 − , H 2 O 2 , HO . ) to cause oxidative stress in the model organism, Escherichia coli , was born. The concept was materialized during our studies on the induction and regulation of the Mn-superoxide dismutase in this unicellular organism. I described how the findings revolutionized the field of oxygen free radicals and oxidative stress and demonstrated its continued relevance and impact to the field today and most probably in the future.}, journal={Archives of Biochemistry and Biophysics}, author={Hassan, Hosni M.}, year={2022}, month={Sep} }
 @article{peacock_hassan_2021, title={Role of the Mn-Catalase in Aerobic Growth of Lactobacillus plantarum ATCC 14431}, url={https://doi.org/10.3390/applmicrobiol1030040}, DOI={10.3390/applmicrobiol1030040}, abstractNote={Lactobacilli are Gram-positive aerotolerant organisms that comprise the largest genus of Lactic Acid Bacteria (LAB). Most lactobacilli are devoid of the antioxidant enzymes, superoxide dismutases, and catalases, required for protection against superoxide radicals and hydrogen peroxide (H2O2), respectively. However, some lactobacilli can accumulate millimolar concentrations of intracellular manganese and spare the need for superoxide dismutase, while others possess non-heme catalases. L. plantarum is associated with plant materials and plays an important role in fermented foods and gut microbiomes. Therefore, understanding the effects of the environment on the growth and survival of this organism is essential for its success in relevant industrial applications. In this report, we investigated the physiological role of Mn-catalase (MnKat) in Lactobacillus plantarum ATCC 14431. To this end, we compared the physiological and morphological properties of a ΔMnkat mutant strain and its isogenic parental strain L. plantarum ATCC 14431. Our data showed that the MnKat is critical for the growth of L. plantarum ATCC 14431 in the presence of oxygen and resistance to H2O2. The aerobic growth of the mutant in presence or absence of H2O2 was improved in the Mn-rich medium (APT) as compared to the growth in MRS medium. Furthermore, under aerobic conditions the mutant strain possessed atypical cellular morphology (i.e., shorter, and fatter). In conclusion, the MnKat of L. plantarum ATCC 14431 is important for aerobic growth, protection against H2O2, and maintenance of the rod-shaped cell morphology under aerobic conditions.}, journal={Applied Microbiology}, author={Peacock, Trent and Hassan, Hosni M.}, year={2021}, month={Dec} }
 @article{troxell_mendoza_ali_koci_hassan_2020, title={Attenuated Salmonella enterica Serovar Typhimurium, Strain NC983, Is Immunogenic, and Protective against Virulent Typhimurium Challenges in Mice}, volume={8}, ISSN={["2076-393X"]}, DOI={10.3390/vaccines8040646}, abstractNote={Non-typhoidal Salmonella (NTS) serovars are significant health burden worldwide. Although much effort has been devoted to developing typhoid-based vaccines for humans, currently there is no NTS vaccine available. Presented here is the efficacy of a live attenuated serovar Typhimurium strain (NC983). Oral delivery of strain NC983 was capable of fully protecting C57BL/6 and BALB/c mice against challenge with virulent Typhimurium. Strain NC983 was found to elicit an anti-Typhimurium IgG response following administration of vaccine and boosting doses. Furthermore, in competition experiments with virulent S. Typhimurium (ATCC 14028), NC983 was highly defective in colonization of the murine liver and spleen. Collectively, these results indicate that strain NC983 is a potential live attenuated vaccine strain that warrants further development.}, number={4}, journal={VACCINES}, author={Troxell, Bryan and Mendoza, Mary and Ali, Rizwana and Koci, Matthew and Hassan, Hosni}, year={2020}, month={Dec} }
 @article{hassan_mendoza_rezvani_koci_dickey_scholl_2020, title={Complete Genome Sequences of Lactobacillus Strains C25 and P38, Isolated from Chicken Cecum}, volume={9}, url={https://doi.org/10.1128/MRA.00501-20}, DOI={10.1128/MRA.00501-20}, abstractNote={We report the complete circular genome sequences of Lactobacillus crispatus strain C25, its plasmid, and Lactobacillus animalis strain P38; both strains were isolated from the cecum of 4-week-old chickens. These isolates represent potential probiotic strains for poultry.}, number={39}, journal={Microbiology Resource Announcements}, publisher={American Society for Microbiology}, author={Hassan, Hosni M. and Mendoza, Mary and Rezvani, Morvarid and Koci, Matthew D. and Dickey, Allison N. and Scholl, Elizabeth H.}, editor={Rasko, DavidEditor}, year={2020}, month={Sep} }
 @article{meinders_mendoza_dickey_scholl_hassan_2020, title={Complete Genome Sequences of Six Lactobacilli Isolated from American Quarter Horses}, volume={9}, ISSN={["2576-098X"]}, url={https://doi.org/10.1128/MRA.00997-20}, DOI={10.1128/MRA.00997-20}, abstractNote={We report the complete circular genome sequences of six Lactobacillus strains and their plasmids, if any, from the fecal material of quarter horses at different ages.}, number={47}, journal={MICROBIOLOGY RESOURCE ANNOUNCEMENTS}, publisher={American Society for Microbiology}, author={Meinders, Rachael I. and Mendoza, Mary and Dickey, Allison N. and Scholl, Elizabeth H. and Hassan, Hosni M.}, editor={Rasko, DavidEditor}, year={2020}, month={Nov} }
 @article{allali_arnold_roach_cadenas_butz_hassan_koci_ballou_mendoza_ali_et al._2017, title={A comparison of sequencing platforms and bioinformatics pipelines for compositional analysis of the gut microbiome}, volume={17}, ISSN={["1471-2180"]}, DOI={10.1186/s12866-017-1101-8}, abstractNote={Advancements in Next Generation Sequencing (NGS) technologies regarding throughput, read length and accuracy had a major impact on microbiome research by significantly improving 16S rRNA amplicon sequencing. As rapid improvements in sequencing platforms and new data analysis pipelines are introduced, it is essential to evaluate their capabilities in specific applications. The aim of this study was to assess whether the same project-specific biological conclusions regarding microbiome composition could be reached using different sequencing platforms and bioinformatics pipelines. Chicken cecum microbiome was analyzed by 16S rRNA amplicon sequencing using Illumina MiSeq, Ion Torrent PGM, and Roche 454 GS FLX Titanium platforms, with standard and modified protocols for library preparation. We labeled the bioinformatics pipelines included in our analysis QIIME1 and QIIME2 (de novo OTU picking [not to be confused with QIIME version 2 commonly referred to as QIIME2]), QIIME3 and QIIME4 (open reference OTU picking), UPARSE1 and UPARSE2 (each pair differs only in the use of chimera depletion methods), and DADA2 (for Illumina data only). GS FLX+ yielded the longest reads and highest quality scores, while MiSeq generated the largest number of reads after quality filtering. Declines in quality scores were observed starting at bases 150–199 for GS FLX+ and bases 90–99 for MiSeq. Scores were stable for PGM-generated data. Overall microbiome compositional profiles were comparable between platforms; however, average relative abundance of specific taxa varied depending on sequencing platform, library preparation method, and bioinformatics analysis. Specifically, QIIME with de novo OTU picking yielded the highest number of unique species and alpha diversity was reduced with UPARSE and DADA2 compared to QIIME. The three platforms compared in this study were capable of discriminating samples by treatment, despite differences in diversity and abundance, leading to similar biological conclusions. Our results demonstrate that while there were differences in depth of coverage and phylogenetic diversity, all workflows revealed comparable treatment effects on microbial diversity. To increase reproducibility and reliability and to retain consistency between similar studies, it is important to consider the impact on data quality and relative abundance of taxa when selecting NGS platforms and analysis tools for microbiome studies.}, journal={BMC MICROBIOLOGY}, author={Allali, Imane and Arnold, Jason W. and Roach, Jeffrey and Cadenas, Maria Belen and Butz, Natasha and Hassan, Hosni M. and Koci, Matthew and Ballou, Anne and Mendoza, Mary and Ali, Rizwana and et al.}, year={2017}, month={Sep} }
 @article{azcarate-peril_butz_cadenas_koci_ballou_mendoza_ali_hassan_2017, title={An Attenuated
                    Salmonella enterica
                    Serovar Typhimurium Strain and Galacto-Oligosaccharides Accelerate Clearance of
                    Salmonella
                    Infections in Poultry through Modifications to the Gut Microbiome}, volume={84}, ISSN={0099-2240 1098-5336}, url={http://dx.doi.org/10.1128/AEM.02526-17}, DOI={10.1128/aem.02526-17}, abstractNote={ABSTRACT Salmonella is estimated to cause one million foodborne illnesses in the United States every year. Salmonella -contaminated poultry products are one of the major sources of salmonellosis. Given the critical role of the gut microbiota in Salmonella transmission, a manipulation of the chicken intestinal microenvironment could prevent animal colonization by the pathogen. In Salmonella , the global regulator gene fnr ( f umarate n itrate r eduction) regulates anaerobic metabolism and is essential for adapting to the gut environment. This study tested the hypothesis that an attenuated Fnr mutant of Salmonella enterica serovar Typhimurium (attST) or prebiotic galacto-oligosaccharides (GOS) could improve resistance to wild-type Salmonella via modifications to the structure of the chicken gut microbiome. Intestinal samples from a total of 273 animals were collected weekly for 9 weeks to evaluate the impact of attST or prebiotic supplementation on microbial species of the cecum, duodenum, jejunum, and ileum. We next analyzed changes to the gut microbiome induced by challenging the animals with a wild-type Salmonella serovar 4,[5],12:r:− (Nal r ) strain and determined the clearance rate of the virulent strain in the treated and control groups. Both GOS and the attenuated Salmonella strain modified the gut microbiome but elicited alterations of different taxonomic groups. The attST produced significant increases of Alistipes and undefined Lactobacillus , while GOS increased Christensenellaceae and Lactobacillus reuteri . The microbiome structural changes induced by both treatments resulted in a faster clearance after a Salmonella challenge. IMPORTANCE With an average annual incidence of 13.1 cases/100,000 individuals, salmonellosis has been deemed a nationally notifiable condition in the United States by the Centers for Disease Control and Prevention (CDC). Earlier studies demonstrated that Salmonella is transmitted by a subset of animals (supershedders). The supershedder phenotype can be induced by antibiotics, ascertaining an essential role for the gut microbiota in Salmonella transmission. Consequently, modulation of the gut microbiota and modification of the intestinal microenvironment could assist in preventing animal colonization by the pathogen. Our study demonstrated that a manipulation of the chicken gut microbiota by the administration of an attenuated Salmonella strain or prebiotic galacto-oligosaccharides (GOS) can promote resistance to Salmonella colonization via increases of beneficial microorganisms that translate into a less hospitable gut microenvironment.}, number={5}, journal={Applied and Environmental Microbiology}, publisher={American Society for Microbiology}, author={Azcarate-Peril, M. Andrea and Butz, Natasha and Cadenas, Maria Belen and Koci, Matthew and Ballou, Anne and Mendoza, Mary and Ali, Rizwana and Hassan, Hosni}, editor={Schottel, Janet L.Editor}, year={2017}, month={Dec} }
 @article{hughes_ali_mendoza_hassan_koci_2017, title={Impact of Dietary Galacto-Oligosaccharide (GOS) on Chicken’s Gut Microbiota, Mucosal Gene Expression, and Salmonella Colonization}, volume={4}, ISSN={2297-1769}, url={http://dx.doi.org/10.3389/fvets.2017.00192}, DOI={10.3389/fvets.2017.00192}, abstractNote={Preventing Salmonella colonization in young birds is key to reducing contamination of poultry products for human consumption (eggs and meat). While several Salmonella vaccines have been developed that are capable of yielding high systemic antibodies, it is not clear how effective these approaches are at controlling or preventing Salmonella colonization of the intestinal tract. Effective alternative control strategies are needed to help supplement the bird's ability to prevent Salmonella colonization, specifically by making the cecum less hospitable to Salmonella. In this study, we investigated the effect of the prebiotic galacto-oligosaccharide (GOS) on the cecal microbiome and ultimately the carriage of Salmonella. Day-old pullet chicks were fed control diets or diets supplemented with GOS (1% w/w) and then challenged with a cocktail of Salmonella Typhimurium and Salmonella Enteritidis. Changes in cecal tonsil gene expression, cecal microbiome, and levels of cecal and extraintestinal Salmonella were assessed at 1, 4, 7, 12, and 27 days post infection. While the Salmonella counts were generally lower in the GOS-treated birds, the differences were not significantly different at the end of the experiment. However, these data demonstrated that treatment with the prebiotic GOS can modify both cecal tonsil gene expression and the cecal microbiome, suggesting that this type of treatment may be useful as a tool for altering the carriage of Salmonella in poultry.}, journal={Frontiers in Veterinary Science}, publisher={Frontiers Media SA}, author={Hughes, Rebecca-Ayme and Ali, Riawana A. and Mendoza, Mary A. and Hassan, Hosni M. and Koci, Matthew D.}, year={2017}, month={Nov} }
 @article{troxell_fink_dickey_scholl_hassan_2016, title={Complete Genome Sequence of NC983, a Live Attenuated Strain of Salmonella enterica Serovar Typhimurium}, volume={4}, ISSN={2169-8287}, url={http://dx.doi.org/10.1128/genomeA.01074-16}, DOI={10.1128/genomeA.01074-16}, abstractNote={ABSTRACT Foodborne infections caused by Salmonella enterica serovars are a significant problem worldwide. Presented here is the genome sequence of the nontyphoidal S. enterica serovar Typhimurium mutant strain NC983, a potential vaccine candidate.}, number={5}, journal={Genome Announcements}, publisher={American Society for Microbiology}, author={Troxell, Bryan and Fink, Ryan C. and Dickey, Allison N. and Scholl, Elizabeth H. and Hassan, Hosni M.}, year={2016}, month={Oct} }
 @book{hassan_2016, title={Designer Probiotic Lactobacilli for use in Farm Animals and Methods for Enrichment and Isolation from any Animal Species or Human}, number={17-063}, author={Hassan, H.}, year={2016}, month={Sep} }
 @article{ballou_ali_mendoza_ellis_hassan_croom_koci_2016, title={Development of the Chick Microbiome: How Early Exposure Influences Future Microbial Diversity}, volume={3}, ISSN={2297-1769}, url={http://dx.doi.org/10.3389/fvets.2016.00002}, DOI={10.3389/fvets.2016.00002}, abstractNote={The concept of improving animal health through improved gut health has existed in food animal production for decades; however, only recently have we had the tools to identify microbes in the intestine associated with improved performance. Currently, little is known about how the avian microbiome develops or the factors that affect its composition. To begin to address this knowledge gap, the present study assessed the development of the cecal microbiome in chicks from hatch to 28 days of age with and without a live Salmonella vaccine and/or probiotic supplement; both are products intended to promote gut health. The microbiome of growing chicks develops rapidly from days 1-3, and the microbiome is primarily Enterobacteriaceae, but Firmicutes increase in abundance and taxonomic diversity starting around day 7. As the microbiome continues to develop, the influence of the treatments becomes stronger. Predicted metagenomic content suggests that, functionally, treatment may stimulate more differences at day 14, despite the strong taxonomic differences at day 28. These results demonstrate that these live microbial treatments do impact the development of the bacterial taxa found in the growing chicks; however, additional experiments are needed to understand the biochemical and functional consequences of these alterations.}, journal={Frontiers in Veterinary Science}, publisher={Frontiers Media SA}, author={Ballou, Anne L. and Ali, Rizwana A. and Mendoza, Mary A. and Ellis, J. C. and Hassan, Hosni M. and Croom, W. J. and Koci, Matthew D.}, year={2016}, month={Jan} }
 @article{rezvani_mendoza_koci_daron_levy_hassan_2016, title={Draft Genome Sequence of Lactobacillus crispatus C25 Isolated from Chicken Cecum}, volume={4}, ISSN={2169-8287}, url={http://dx.doi.org/10.1128/genomeA.01223-16}, DOI={10.1128/genomeA.01223-16}, abstractNote={ABSTRACT Lactic acid bacteria are important members of the gut microbiota of humans and animals. Here, we present the genome sequence of Lactobacillus crispatus strain C25, originally isolated from the cecum of 4-week-old chicken fed a standard diet. This isolate represents a potential probiotic strain for poultry.}, number={6}, journal={Genome Announcements}, publisher={American Society for Microbiology}, author={Rezvani, Morvarid and Mendoza, Mary and Koci, Matthew D. and Daron, Caitlyn and Levy, Josh and Hassan, Hosni M.}, year={2016}, month={Dec} }
 @article{rezvani_mendoza_koci_daron_levy_hassan_2016, title={Draft Genome Sequences of Lactobacillus animalis Strain P38 and Lactobacillus reuteri Strain P43 Isolated from Chicken Cecum}, volume={4}, ISSN={2169-8287}, url={http://dx.doi.org/10.1128/genomeA.01229-16}, DOI={10.1128/genomeA.01229-16}, abstractNote={ABSTRACT Here, we present the genome sequence of Lactobacillus animalis strain P38 and Lactobacillus reuteri strain P43, both isolated from the cecum content of a 4-week old chicken fed a diet supplemented with the prebiotic β(1-4)galacto-oligosaccharide (GOS). These indigenous Lactobacillus isolates are potential probiotic organisms for poultry.}, number={6}, journal={Genome Announcements}, publisher={American Society for Microbiology}, author={Rezvani, Morvarid and Mendoza, Mary and Koci, Matthew D. and Daron, Caitlyn and Levy, Josh and Hassan, Hosni M.}, year={2016}, month={Dec} }
 @book{hassan_troxell_2016, title={Engineered Salmonella Serovar Typhimurium Strains, Compositions Thereof, and Methods of Use}, number={62/368,507}, author={Hassan, H.M. and Troxell, S.B.}, year={2016}, month={Jul} }
 @inbook{troxell_hassan_2016, place={Hoboken, New Jersey}, title={Interplay Between O2 and Iron in Gene Expression: Environmental Sensing by FNR, ArcA, and Fur in Bacteria}, ISBN={9781119004813 9781119004882}, url={http://dx.doi.org/10.1002/9781119004813.ch105}, DOI={10.1002/9781119004813.ch105}, abstractNote={Nearly all bacterial cells require iron as an essential cofactor for enzymatic reactions. However, the availability of iron is dependent on the environmental conditions. In aerobic environments, oxygen (O2) reacts with soluble ferrous iron (Fe2+) to form insoluble ferric iron (Fe3+). Bacteria and other organisms have evolved to exploit the reaction of O2 with iron to regulate their adaptation to changes in O2 concentrations. Not surprisingly, this involves transcription factors that directly or indirectly sense the redox state. The bacterial transcription factors fumarate nitrate reduction (FNR) and ferric uptake regulator (Fur) are examples of the ones that use iron as a cofactor, whereas the response regulator anoxic respiratory control (ArcA) is an example of one that indirectly senses the redox. Many bacterial pathogens encode fnr, arcA, and fur homologs that sense the environmental O2 and Fe state and accordingly regulate metabolism and responses to oxidative stress. In many cases, these three transcription factors regulate the transition from aerobic to anaerobic conditions, and vice versa. In pathogens, there is evidence that virulence is also regulated by one or more of these three transcription factors, indicating the critical roles of the redox state and iron concentrations in pathogenesis. This chapter focuses on the contributions of FNR, ArcA, and Fur to virulence in bacterial pathogens.}, booktitle={Stress and Environmental Regulation of Gene Expression and Adaptation in Bacteria, I&II}, publisher={John Wiley & Sons, Inc.}, author={Troxell, B. and Hassan, H.M.}, editor={de Bruijn, Frans J.Editor}, year={2016}, month={Aug}, pages={1079–1089} }
 @inproceedings{hassan_2016, title={The Chicken Gut Microbiome and Salmonella}, author={Hassan, H.M.}, year={2016} }
 @misc{hassan_2016, title={Use of Probiotics and prebiotics in Poultry}, author={Hassan, H}, year={2016}, month={Oct} }
 @book{hassan_2016, title={Utilization of Hydroxyl Radicalfor Accelerated Shelf-life Testing}, number={16-275}, author={Hassan, H.}, year={2016}, month={Apr} }
 @article{leite_troxell_bruno-bárcena_hassan_2015, title={Biology of reactive oxygen species, oxidative stress, and antioxidants in lactic acid bacteria}, url={https://publons.com/publon/31684350/}, DOI={10.21775/9781910190098.14}, journal={Probiotics and Prebiotics: Current Research and Future Trends}, author={Leite, M. C. T. and Troxell, B. and Bruno-Bárcena, José M and Hassan, Hosni}, year={2015}, pages={205–218} }
 @article{caldwell_pérez-díaz_sandeep_simunovic_harris_osborne_hassan_2015, title={Mitochondrial DNA Fragmentation as a Molecular Tool to Monitor Thermal Processing of Plant-Derived, Low-Acid Foods, and Biomaterials}, volume={80}, ISSN={0022-1147}, url={http://dx.doi.org/10.1111/1750-3841.12937}, DOI={10.1111/1750-3841.12937}, abstractNote={Cycle threshold (Ct) increase, quantifying plant-derived DNA fragmentation, was evaluated for its utility as a time-temperature integrator. This novel approach to monitoring thermal processing of fresh, plant-based foods represents a paradigm shift. Instead of using quantitative polymerase chain reaction (qPCR) to detect pathogens, identify adulterants, or authenticate ingredients, this rapid technique was used to quantify the fragmentation of an intrinsic plant mitochondrial DNA (mtDNA) gene over time-temperature treatments. Universal primers were developed which amplified a mitochondrial gene common to plants (atp1). These consensus primers produced a robust qPCR signal in 10 vegetables, 6 fruits, 3 types of nuts, and a biofuel precursor. Using sweet potato (Ipomoea batatas) puree as a model low-acid product and simple linear regression, Ct value was highly correlated to time-temperature treatment (R(2) = 0.87); the logarithmic reduction (log CFU/mL) of the spore-forming Clostridium botulinum surrogate, Geobacillus stearothermophilus (R(2) = 0.87); and cumulative F-value (min) in a canned retort process (R(2) = 0.88), all comparisons conducted at 121 °C. D121 and z-values were determined for G. stearothermophilus ATCC 7953 and were 2.71 min and 11.0 °C, respectively. D121 and z-values for a 174-bp universal plant amplicon were 11.3 min and 9.17 °C, respectively, for mtDNA from sweet potato puree. We present these data as proof-of-concept for a molecular tool that can be used as a rapid, presumptive method for monitoring thermal processing in low-acid plant products.}, number={8}, journal={Journal of Food Science}, publisher={Wiley}, author={Caldwell, Jane M. and Pérez-Díaz, Ilenys M. and Sandeep, KP and Simunovic, Josip and Harris, Keith and Osborne, Jason A. and Hassan, Hosni M.}, year={2015}, month={Jul}, pages={M1804–M1814} }
 @article{caldwell_pérez-díaz_harris_hassan_simunovic_sandeep_2015, title={Mitochondrial DNA Fragmentation to Monitor Processing Parameters in High Acid, Plant-Derived Foods}, volume={80}, ISSN={0022-1147}, url={http://dx.doi.org/10.1111/1750-3841.13139}, DOI={10.1111/1750-3841.13139}, abstractNote={Mitochondrial DNA (mtDNA) fragmentation was assessed in acidified foods. Using quantitative polymerase chain reaction, Ct values measured from fresh, fermented, pasteurized, and stored cucumber mtDNA were determined to be significantly different (P > 0.05) based on processing and shelf-life. This indicated that the combination of lower temperature thermal processes (hot-fill at 75 °C for 15 min) and acidified conditions (pH = 3.8) was sufficient to cause mtDNA fragmentation. In studies modeling high acid juices, pasteurization (96 °C, 0 to 24 min) of tomato serum produced Ct values which had high correlation to time-temperature treatment. Primers producing longer amplicons (approximately 1 kb) targeting the same mitochondrial gene gave greater sensitivity in correlating time-temperature treatments to Ct values. Lab-scale pasteurization studies using Ct values derived from the longer amplicon differentiated between heat treatments of tomato serum (95 °C for <2 min). MtDNA fragmentation was shown to be a potential new tool to characterize low temperature (<100 °C) high acid processes (pH < 4.6), nonthermal processes such as vegetable fermentation and holding times of acidified, plant-derived products. This method could be used as a tool for hot-fill process validation, monitoring of vegetable fermentations, and holding times of acidic plant-derived products. Mitochondrial DNA is universally found and easily extracted from all plant products. Processors will be able to validate processes and track process deviations using rapid molecular methods. Processors can use this presumptive test prior to shipping out a product.}, number={12}, journal={Journal of Food Science}, publisher={Wiley}, author={Caldwell, Jane M. and Pérez-Díaz, Ilenys M. and Harris, Keith and Hassan, Hosni M. and Simunovic, Josip and Sandeep, K.P.}, year={2015}, month={Nov}, pages={M2892–M2898} }
 @article{troxell_petri_daron_pereira_mendoza_hassan_koci_2015, title={Poultry Body Temperature Contributes to Invasion Control through Reduced Expression of Salmonella Pathogenicity Island 1 Genes in Salmonella enterica Serovars Typhimurium and Enteritidis}, volume={81}, ISSN={0099-2240 1098-5336}, url={http://dx.doi.org/10.1128/AEM.02622-15}, DOI={10.1128/aem.02622-15}, abstractNote={ABSTRACT Salmonella enterica serovars Typhimurium ( S . Typhimurium) and Enteritidis ( S . Enteritidis) are foodborne pathogens, and outbreaks are often associated with poultry products. Chickens are typically asymptomatic when colonized by these serovars; however, the factors contributing to this observation are uncharacterized. Whereas symptomatic mammals have a body temperature between 37°C and 39°C, chickens have a body temperature of 41°C to 42°C. Here, in vivo experiments using chicks demonstrated that numbers of viable S . Typhimurium or S . Enteritidis bacteria within the liver and spleen organ sites were ≥4 orders of magnitude lower than those within the ceca. When similar doses of S . Typhimurium or S . Enteritidis were given to C3H/HeN mice, the ratio of the intestinal concentration to the liver/spleen concentration was 1:1. In the avian host, this suggested poor survival within these tissues or a reduced capacity to traverse the host epithelial layer and reach liver/spleen sites or both. Salmonella pathogenicity island 1 (SPI-1) promotes localization to liver/spleen tissues through invasion of the epithelial cell layer. Following in vitro growth at 42°C, SPI-1 genes sipC , invF , and hilA and the SPI-1 rtsA activator were downregulated compared to expression at 37°C. Overexpression of the hilA activators fur , fliZ , and hilD was capable of inducing hilA-lacZ at 37°C but not at 42°C despite the presence of similar levels of protein at the two temperatures. In contrast, overexpression of either hilC or rtsA was capable of inducing hilA and sipC at 42°C. These data indicate that physiological parameters of the poultry host, such as body temperature, have a role in modulating expression of virulence.}, number={23}, journal={Applied and Environmental Microbiology}, publisher={American Society for Microbiology}, author={Troxell, Bryan and Petri, Nicholas and Daron, Caitlyn and Pereira, Rafaela and Mendoza, Mary and Hassan, Hosni M. and Koci, Matthew D.}, editor={Elkins, C. A.Editor}, year={2015}, month={Sep}, pages={8192–8201} }
 @book{hassan_2014, title={A vector for vaccination against Lyme Disease and other insect transmitted diseases using a live Salmonella vaccine}, author={Hassan, H.}, year={2014}, month={May} }
 @inproceedings{allali_cadenas_ballou_mendoza_ali_hassan_koci_azcarate-peril_2014, title={Comparative analysis of 16S amplicon sequencing data from Roche 454 and Ion Torrent PGM platforms}, author={Allali, Imane and Cadenas, Maria Belen and Ballou, Anne and Mendoza, Mary and Ali, Rizwana and Hassan, Hosni and Koci, Matthew and Azcarate-Peril, M. Andrea}, year={2014}, month={May} }
 @inproceedings{ballou_ali_mendoza_hassan_koci_2014, title={Development of the chick microbiome: How early exposure influences future microbial diversity}, author={Ballou, A.L. and Ali, R. and Mendoza, M. and Hassan, H. and Koci, M.D.}, year={2014} }
 @article{husain_jones-carson_liu_song_saah_troxell_mendoza_hassan_vazquez-torresa_2014, title={Ferric Uptake Regulator-Dependent Antinitrosative Defenses in Salmonella enterica Serovar Typhimurium Pathogenesis}, volume={82}, ISSN={["1098-5522"]}, DOI={10.1128/iai.01201-13}, abstractNote={ABSTRACT Herein we report an important role for the ferric uptake regulator (Fur) in the resistance of Salmonella enterica serovar Typhimurium to the reactive nitrogen species produced by inducible nitric oxide (NO) synthase in an NRAMP1 r murine model of acute systemic infection. The expression of fur protected Salmonella grown under normoxic and hypoxic conditions against the bacteriostatic activity of NO. The hypersusceptibility of fur -deficient Salmonella to the cytotoxic actions of NO coincides with a marked repression of respiratory activity and the reduced ability of the bacteria to detoxify NO. A fur mutant Salmonella strain contained reduced levels of the terminal quinol oxidases of the electron transport chain. Addition of the heme precursor δ-aminolevulinic acid restored the cytochrome content, respiratory activity, NO consumption, and wild-type growth in bacteria undergoing nitrosative stress. The innate antinitrosative defenses regulated by Fur added to the adaptive response associated with the NO-detoxifying activity of the flavohemoprotein Hmp. Our investigations indicate that, in addition to playing a critical role in iron homeostasis, Fur is an important antinitrosative determinant of Salmonella pathogenesis.}, number={1}, journal={INFECTION AND IMMUNITY}, author={Husain, Maroof and Jones-Carson, Jessica and Liu, Lin and Song, Miryoung and Saah, J. Royden and Troxell, Bryan and Mendoza, Mary and Hassan, Hosni and Vazquez-Torresa, Andres}, year={2014}, month={Jan}, pages={333–340} }
 @article{troxell_zhang_bourret_zeng_blum_gherardini_hassan_yang_2014, title={Pyruvate Protects Pathogenic Spirochetes from H2O2 Killing}, volume={9}, ISSN={1932-6203}, url={http://dx.doi.org/10.1371/journal.pone.0084625}, DOI={10.1371/journal.pone.0084625}, abstractNote={Pathogenic spirochetes cause clinically relevant diseases in humans and animals, such as Lyme disease and leptospirosis. The causative agent of Lyme disease, Borrelia burgdorferi, and the causative agent of leptospirosis, Leptospria interrogans, encounter reactive oxygen species (ROS) during their enzootic cycles. This report demonstrated that physiologically relevant concentrations of pyruvate, a potent H2O2 scavenger, and provided passive protection to B. burgdorferi and L. interrogans against H2O2. When extracellular pyruvate was absent, both spirochetes were sensitive to a low dose of H2O2 (≈0.6 µM per h) generated by glucose oxidase (GOX). Despite encoding a functional catalase, L. interrogans was more sensitive than B. burgdorferi to H2O2 generated by GOX, which may be due to the inherent resistance of B. burgdorferi because of the virtual absence of intracellular iron. In B. burgdorferi, the nucleotide excision repair (NER) and the DNA mismatch repair (MMR) pathways were important for survival during H2O2 challenge since deletion of the uvrB or the mutS genes enhanced its sensitivity to H2O2 killing; however, the presence of pyruvate fully protected ΔuvrB and ΔmutS from H2O2 killing further demonstrating the importance of pyruvate in protection. These findings demonstrated that pyruvate, in addition to its classical role in central carbon metabolism, serves as an important H2O2 scavenger for pathogenic spirochetes. Furthermore, pyruvate reduced ROS generated by human neutrophils in response to the Toll-like receptor 2 (TLR2) agonist zymosan. In addition, pyruvate reduced neutrophil-derived ROS in response to B. burgdorferi, which also activates host expression through TLR2 signaling. Thus, pathogenic spirochetes may exploit the metabolite pyruvate, present in blood and tissues, to survive H2O2 generated by the host antibacterial response generated during infection.}, number={1}, journal={PLoS ONE}, publisher={Public Library of Science (PLoS)}, author={Troxell, Bryan and Zhang, Jun-Jie and Bourret, Travis J. and Zeng, Melody Yue and Blum, Janice and Gherardini, Frank and Hassan, Hosni M. and Yang, X. Frank}, editor={Wooten, Ronald MarkEditor}, year={2014}, month={Jan}, pages={e84625} }
 @inproceedings{hassan_2014, title={The Chicken Gut Microbiome and Salmonella}, author={Hassan, H.M.}, year={2014}, month={Oct} }
 @book{hassan_fink_evans_2013, title={Attenuated FNR deficient enterobacteria}, number={US8435506B2}, author={Hassan, H. and Fink, R.C. and Evans, M.R.}, year={2013}, month={May} }
 @misc{troxell_hassan_2013, title={Transcriptional regulation by Ferric Uptake Regulator (Fur) in pathogenic bacteria}, volume={3}, ISSN={["2235-2988"]}, DOI={10.3389/fcimb.2013.00059}, abstractNote={REVIEW article Front. Cell. Infect. Microbiol., 02 October 2013Sec. Bacteria and Host Volume 3 - 2013 | https://doi.org/10.3389/fcimb.2013.00059}, journal={FRONTIERS IN CELLULAR AND INFECTION MICROBIOLOGY}, author={Troxell, Bryan and Hassan, Hosni M.}, year={2013}, month={Oct} }
 @book{hassan_fink_evans_2012, title={Attenuated FNR Deficient Enterobacteria}, number={8,101,168}, author={Hassan, H. and Fink, R.C. and Evans, M.R.}, year={2012}, month={Jan} }
 @article{qiu_croom_ali_ballou_smith_ashwell_hassan_chiang_koci_2012, title={Direct fed microbial supplementation repartitions host energy to the immune system}, volume={90}, ISSN={["1525-3163"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84865634686&partnerID=MN8TOARS}, DOI={10.2527/jas.2011-4611}, abstractNote={Direct fed microbials and probiotics are used to promote health in livestock and poultry; however, their mechanism of action is still poorly understood. We previously reported that direct fed microbial supplementation in young broilers reduced ileal respiration without changing whole-body energy expenditure. The current studies were conducted to further investigate the effects of a direct fed microbial on energy metabolism in different tissues of broilers. One hundred ninety-two 1-d-old broiler chicks (16 chicks/pen) were randomly assigned to 2 dietary groups: standard control starter diet (CSD) and CSD plus direct fed microbial (DFMD; 0.3%) with 6 pens/treatment. Body weight, feed consumption, whole-body energy expenditure, organ mass, tissue respiration rates, and peripheral blood mononuclear cell (PBMC) ATP concentrations were measured to estimate changes in energy metabolism. No differences in whole body energy expenditure or BW gain were observed; however, decreased ileal O2 respiration (P < 0.05) was measured in DFMD fed broilers. In contrast, the respiration rate of the thymus in those broilers was increased (P < 0.05). The PBMC from DFMD fed broilers had increased ATP concentrations and exhibited increased ATP turnover (P < 0.01). To determine if the increased energy consumption by PBMC corresponded with an altered immune response, broilers were immunized with sheep red blood cells (SRBC) and assayed for differences in their humoral response. The DFMD-fed broilers had a faster rate of antigen specific IgG production (P < 0.05) and an increase in total IgA (P < 0.05). Collectively, these data indicate that supplementation with the direct fed microbial used in this study resulted in energy re-partitioning to the immune system and an increase in antibody production independent of changes in whole body metabolism or growth performance.}, number={8}, journal={JOURNAL OF ANIMAL SCIENCE}, author={Qiu, R. and Croom, J. and Ali, R. A. and Ballou, A. L. and Smith, C. D. and Ashwell, C. M. and Hassan, H. M. and Chiang, C. -C. and Koci, M. D.}, year={2012}, month={Aug}, pages={2639–2651} }
 @article{evans_fink_vazquez-torres_porwollik_jones-carson_mcclelland_hassan_2011, title={Analysis of the ArcA regulon in anaerobically grown Salmonella enterica sv. Typhimurium}, volume={11}, ISSN={["1471-2180"]}, DOI={10.1186/1471-2180-11-58}, abstractNote={Abstract Background Salmonella enterica serovar Typhimurium ( S . Typhimurium) is a Gram-negative pathogen that must successfully adapt to the broad fluctuations in the concentration of dissolved dioxygen encountered in the host. In Escherichia coli , ArcA ( A erobic R espiratory C ontrol) helps the cells to sense and respond to the presence of dioxygen. The global role of ArcA in E. coli is well characterized; however, little is known about its role in anaerobically grown S . Typhimurium. Results We compared the transcriptional profiles of the virulent wild-type (WT) strain (ATCC 14028s) and its isogenic arcA mutant grown under anaerobic conditions. We found that ArcA directly or indirectly regulates 392 genes (8.5% of the genome); of these, 138 genes are poorly characterized. Regulation by ArcA in S . Typhimurium is similar, but distinct from that in E . coli . Thus, genes/operons involved in core metabolic pathways (e.g., succinyl-CoA, fatty acid degradation, cytochrome oxidase complexes, flagellar biosynthesis, motility, and chemotaxis) were regulated similarly in the two organisms. However, genes/operons present in both organisms, but regulated differently by ArcA in S . Typhimurium included those coding for ethanolamine utilization, lactate transport and metabolism, and succinate dehydrogenases. Salmonella -specific genes/operons regulated by ArcA included those required for propanediol utilization, flagellar genes ( mcpAC , cheV ), Gifsy-1 prophage genes, and three SPI-3 genes ( mgtBC , slsA , STM3784). In agreement with our microarray data, the arcA mutant was non-motile, lacked flagella, and was as virulent in mice as the WT. Additionally, we identified a set of 120 genes whose regulation was shared with the anaerobic redox regulator, Fnr. Conclusion(s) We have identified the ArcA regulon in anaerobically grown S . Typhimurium. Our results demonstrated that in S . Typhimurium, ArcA serves as a transcriptional regulator coordinating cellular metabolism, flagella biosynthesis, and motility. Furthermore, ArcA and Fnr share in the regulation of 120 S . Typhimurium genes.}, journal={BMC MICROBIOLOGY}, author={Evans, Matthew R. and Fink, Ryan C. and Vazquez-Torres, Andres and Porwollik, Steffen and Jones-Carson, Jessica and McClelland, Michael and Hassan, Hosni M.}, year={2011}, month={Mar} }
 @article{troxell_sikes_fink_vazquez-torres_jones-carson_hassan_2011, title={Fur Negatively Regulates hns and Is Required for the Expression of HilA and Virulence in Salmonella enterica Serovar Typhimurium}, volume={193}, ISSN={["1098-5530"]}, DOI={10.1128/jb.00942-10}, abstractNote={ABSTRACT Iron is an essential element for the survival of living cells. However, excess iron is toxic, and its uptake is exquisitely regulated by the ferric uptake regulator, Fur. In Salmonella , the Salmonella pathogenicity island 1 (SPI-1) encodes a type three secretion system, which is required for invasion of host epithelial cells in the small intestine. A major activator of SPI-1 is HilA, which is encoded within SPI-1. One known regulator of hilA is Fur. The mechanism of hilA regulation by Fur is unknown. We report here that Fur is required for virulence in Salmonella enterica serovar Typhimurium and that Fur is required for the activation of hilA , as well as of other HilA-dependent genes, invF and sipC . The Fur-dependent regulation of hilA was independent of PhoP, a known repressor of hilA . Instead, the expression of the gene coding for the histone-like protein, hns , was significantly derepressed in the fur mutant. Indeed, the activation of hilA by Fur was dependent on 28 nucleotides located upstream of hns . Moreover, we used chromatin immunoprecipitation to show that Fur bound, in vivo , to the upstream region of hns in a metal-dependent fashion. Finally, deletion of fur in an hns mutant resulted in Fur-independent activation of hilA . In conclusion, Fur activates hilA by repressing the expression of hns .}, number={2}, journal={JOURNAL OF BACTERIOLOGY}, author={Troxell, Bryan and Sikes, Michael L. and Fink, Ryan C. and Vazquez-Torres, Andres and Jones-Carson, Jessica and Hassan, Hosni M.}, year={2011}, month={Jan}, pages={497–505} }
 @article{troxell_fink_porwollik_mcclelland_hassan_2011, title={The Fur regulon in anaerobically grown Salmonella enterica sv. Typhimurium: identification of new Fur targets}, volume={11}, ISSN={["1471-2180"]}, DOI={10.1186/1471-2180-11-236}, abstractNote={The Ferric uptake regulator (Fur) is a transcriptional regulator that controls iron homeostasis in bacteria. Although the regulatory role of Fur in Escherichia coli is well characterized, most of the studies were conducted under routine culture conditions, i.e., in ambient oxygen concentration. To reveal potentially novel aspects of the Fur regulon in Salmonella enterica serovar Typhimurium under oxygen conditions similar to that encountered in the host, we compared the transcriptional profiles of the virulent wild-type strain (ATCC 14028s) and its isogenic Δfur strain under anaerobic conditions.Microarray analysis of anaerobically grown Δfur S. Typhimurium identified 298 differentially expressed genes. Expression of several genes controlled by Fnr and NsrR appeared to be also dependent on Fur. Furthermore, Fur was required for the activity of the cytoplasmic superoxide disumutases (MnSOD and FeSOD). The regulation of FeSOD gene, sodB, occurred via small RNAs (i.e., the ryhB homologs, rfrA and rfrB) with the aid of the RNA chaperone Hfq. The transcription of sodA was increased in Δfur; however, the enzyme was inactive due to the incorporation of iron instead of manganese in SodA. Additionally, in Δfur, the expression of the gene coding for the ferritin-like protein (ftnB) was down-regulated, while the transcription of the gene coding for the nitric oxide (NO·) detoxifying flavohemoglobin (hmpA) was up-regulated. The promoters of ftnB and hmpA do not contain recognized Fur binding motifs, which indicated their probable indirect regulation by Fur. However, Fur activation of ftnB was independent of Fnr. In addition, the expression of the gene coding for the histone-like protein, H-NS (hns) was increased in Δfur. This may explain the observed down-regulation of the tdc operon, responsible for the anaerobic degradation of threonine, and ftnB in Δfur.This study determined that Fur is a positive factor in ftnB regulation, while serving to repress the expression of hmpA. Furthermore, Fur is required for the proper expression and activation of the antioxidant enzymes, FeSOD and MnSOD. Finally, this work identified twenty-six new targets of Fur regulation, and demonstrates that H-NS repressed genes are down-regulated in Δfur.}, journal={BMC MICROBIOLOGY}, author={Troxell, Bryan and Fink, Ryan C. and Porwollik, Steffen and McClelland, Michael and Hassan, Hosni M.}, year={2011}, month={Oct} }
 @article{dobrogosz_peacock_hassan_2010, title={Evolution of the Probiotic Concept: From Conception to Validation and Acceptance in Medical Science}, volume={72}, ISBN={["978-0-12-380989-6"]}, ISSN={["0065-2164"]}, DOI={10.1016/s0065-2164(10)72001-3}, abstractNote={Two pioneering achievements by Ilya Ilyich Metchnikoff were recorded in 1908. Most notable was his Nobel Prize in Medicine for discovering the innate cellular immune response to an infectious challenge. Of lesser note was his recommendation, "...to absorb large quantities of microbes, as a general belief is that microbes are harmful. This belief is erroneous. There are many useful microbes, amongst which the lactic bacilli have an honorable place." While his discovery of the inflammatory response was rapidly incorporated into our understanding of cellular immunity, his recommendation "to absorb large quantities of microbes," on the other hand, languished for decades in limbos of indifference, skepticism, and disbelief. The present chapter is a synopsis of salient discoveries made during the past 100 years, which gradually displaced these skepticisms, validated his concept of "useful microbes," and propelled his "lactic bacilli" into the mainstream of modern medical science, practice, and therapy.}, journal={ADVANCES IN APPLIED MICROBIOLOGY, VOL 72}, author={Dobrogosz, Walter J. and Peacock, Trent J. and Hassan, Hosni M.}, year={2010}, pages={1–41} }
 @article{bruno-barcena_azcarate-peril_hassan_2010, title={Role of Antioxidant Enzymes in Bacterial Resistance to Organic Acids}, volume={76}, ISSN={["1098-5336"]}, url={http://europepmc.org/abstract/med/20305033}, DOI={10.1128/aem.02718-09}, abstractNote={Growth in aerobic environments has been shown to generate reactive oxygen species (ROS) and to cause oxidative stress in most organisms. Antioxidant enzymes (i.e., superoxide dismutases and hydroperoxidases) and DNA repair mechanisms provide protection against ROS. Acid stress has been shown to be associated with the induction of Mn superoxide dismutase (MnSOD) in Lactococcus lactis and Staphylococcus aureus. However, the relationship between acid stress and oxidative stress is not well understood. In the present study, we showed that mutations in the gene coding for MnSOD (sodA) increased the toxicity of lactic acid at pH 3.5 in Streptococcus thermophilus. The inclusion of the iron chelators 2,2'-dipyridyl (DIP), diethienetriamine-pentaacetic acid (DTPA), and O-phenanthroline (O-Phe) provided partial protection against 330 mM lactic acid at pH 3.5. The results suggested that acid stress triggers an iron-mediated oxidative stress that can be ameliorated by MnSOD and iron chelators. These findings were further validated in Escherichia coli strains lacking both MnSOD and iron SOD (FeSOD) but expressing a heterologous MnSOD from S. thermophilus. We also found that, in E. coli, FeSOD did not provide the same protection afforded by MnSOD and that hydroperoxidases are equally important in protecting the cells against acid stress. These findings may explain the ability of some microorganisms to survive better in acidified environments, as in acid foods, during fermentation and accumulation of lactic acid or during passage through the low pH of the stomach.}, number={9}, journal={APPLIED AND ENVIRONMENTAL MICROBIOLOGY}, author={Bruno-Barcena, Jose M. and Azcarate-Peril, M. Andrea and Hassan, Hosni M.}, year={2010}, month={May}, pages={2747–2753} }
 @article{clare_zheng_hassan_swaisgood_catignani_2008, title={Antimicrobial properties of milkfat globule membrane fractions}, volume={71}, ISSN={["1944-9097"]}, DOI={10.4315/0362-028X-71.1.126}, abstractNote={Milkfat globule membranes (MFGMs) were prepared from bovine cream according to standard procedures. These membranes and peptide hydrolysates, which were generated by proteolysis with immobilized digestive enzymes, were screened for antibacterial activity against Escherichia coli O157:H7, Listeria monocytogenes, Salmonella enterica Typhimurium, Pseudomonas fluorescens, Bacillus cereus, Lactobacillus acidophilus, and Lactobacillus gasseri. Assays were first performed on beef heart infusion (BHI) plates spotted with test protein-peptide fractions and then seeded with lawns of indicator cells to monitor the zone of growth inhibition. Under these experimental conditions, MFGMs were most active against Salmonella Typhimurium and P. fluorescens. However, antibacterial activity was not seen after plating on Luria-Bertani (LB) medium. We determined that the antimicrobial effects observed on BHI plates were due to the generation of H2O2 by xanthine oxidase, a major protein constituent of the MFGMs, as a result of purine catalysis. This substrate is present in BHI but lacking in LB medium. Evaluation of purified xanthine oxidase alone resulted in analogous data trends. The growth of probiotic Lactobacillus strains were affected only marginally when grown on lactobacilli deMan Rogosa Sharpe plates, suggesting the decreased sensitivity of these bacteria to H2O2. In this study, several MFGM hydrolysates exhibited variable antibacterial activity against test food pathogens on agar plates prepared with M9 minimal media, and this variation was not attributable to xanthine oxidase enzymatic activity. The probiotic microorganisms were mostly resilient to these antibacterial fractions. Bovine MFGM fractions may represent an excellent resource material from which to generate native, naturally occurring biodefensive proteins and/or peptides.}, number={1}, journal={JOURNAL OF FOOD PROTECTION}, author={Clare, Debra A. and Zheng, Zuoxing and Hassan, Hosni M. and Swaisgood, Harold E. and Catignani, George L.}, year={2008}, month={Jan}, pages={126–133} }
 @article{kreske_bjornsdottir_breidt_hassan_2008, title={Effects of pH, Dissolved Oxygen, and Ionic Strength on the Survival of Escherichia coli O157:H7 in Organic Acid Solutions}, volume={71}, ISSN={["1944-9097"]}, DOI={10.4315/0362-028X-71.12.2404}, abstractNote={The ability of Escherichia coli O157:H7 to survive in acidified vegetable products is of concern because of previously documented outbreaks associated with fruit juices. A study was conducted to determine the survival of E. coli O157:H7 in organic acids at pH values typical of acidified vegetable products (pH 3.2 and 3.7) under different dissolved oxygen conditions (< or = 0.05 and 5 mg/liter) and a range of ionic strengths (0.086 to 1.14). All solutions contained 20 mM gluconic acid, which was used as a noninhibitory low pH buffer to compare the individual acid effect to that of pH alone on the survival of E. coli O157:H7. E. coli O157:H7 cells challenged in buffered solution with ca. 5-mg/liter dissolved oxygen (present in tap water) over a range of ionic strengths at pH 3.2 exhibited a decrease in survival over 6 h at 30 degrees C as the ionic strength was increased. Cells challenged in 40 mM protonated L-lactic and acetic acid solutions with ionic strength of 0.684 achieved a > 4.7-log CFU/ml reduction at pH 3.2. However, under oxygen-limiting conditions in an anaerobic chamber, with < or = 0.05-mg/ liter oxygen, E. coli O157:H7 cells showed < or = 1.55-log CFU/ml reduction regardless of pH, acid type, concentration, or ionic strength. Many acid and acidified foods are sold in hermetically sealed containers with oxygen-limiting conditions. Our results demonstrate that E. coli O157:H7 may survive better than previously expected from studies with acid solutions containing dissolved oxygen.}, number={12}, journal={JOURNAL OF FOOD PROTECTION}, author={Kreske, Audrey C. and Bjornsdottir, Kristin and Breidt, Fred, Jr. and Hassan, Hosni}, year={2008}, month={Dec}, pages={2404–2409} }
 @article{carroll_andrus_bruno-barcena_klaenhammer_hassan_threadgill_2007, title={Anti-inflammatory properties of Lactobacillus gasseri expressing manganese superoxide dismutase using the interleukin 10-deficient mouse model of colitis}, volume={293}, ISSN={["1522-1547"]}, url={http://europepmc.org/abstract/med/17640978}, DOI={10.1152/ajpgi.00132.2007}, abstractNote={Emerging evidence has implicated reactive oxygen species (ROS) in the pathogenesis of inflammatory bowel disease (IBD). Although intestinal epithelial cells produce the ROS-neutralizing enzyme superoxide dismutase (SOD), the protein and activity levels of copper/zinc (Cu/Zn) and manganese (Mn) SOD are perturbed in inflamed tissues of IBD patients. Thus we investigated the ability of MnSOD from Streptococcus thermophilus to reduce colitis symptoms in interleukin (IL) 10-deficient mice using Lactobacillus gasseri as a delivery vehicle. Cohorts of 13–15 IL-10-deficient mice were left untreated or supplemented with native L. gasseri or L. gasseri expressing MnSOD for 4 wk. Colonic tissue was collected and inflammation was histologically scored. The presence of innate immune cells was investigated by immunohistochemistry and the host antioxidant response was determined by quantitative PCR. It was demonstrated that L. gasseri was stably maintained in mice for at least 3 days. L. gasseri producing MnSOD significantly reduced inflammation in IL-10-deficient mice compared with untreated controls ( P < 0.05), whereas the anti-inflammatory effects of both native and MnSOD producing L. gasseri were more pronounced in males. The anti-inflammatory effects of L. gasseri were associated with a reduction in the infiltration of neutrophils and macrophages. Transcripts of antioxidant genes were equivalent in colonic tissues obtained from control and probiotic-treated IL-10-deficient mice. This study demonstrates that L. gasseri producing MnSOD has significant anti-inflammatory activity that reduces the severity of colitis in the IL-10-deficient mouse.}, number={4}, journal={AMERICAN JOURNAL OF PHYSIOLOGY-GASTROINTESTINAL AND LIVER PHYSIOLOGY}, author={Carroll, Ian M. and Andrus, Jason M. and Bruno-Barcena, Jose M. and Klaenhammer, Todd R. and Hassan, Hosni M. and Threadgill, Deborah S.}, year={2007}, month={Oct}, pages={G729–G738} }
 @article{fink_evans_porwollik_vazquez-torres_jones-carson_troxell_libby_mcclelland_hassan_2007, title={FNR is a global regulator of virulence and anaerobic metabolism in Salmonella enterica serovar typhimurium (ATCC 14028s)}, volume={189}, ISSN={["1098-5530"]}, DOI={10.1128/JB.00726-06}, abstractNote={ABSTRACT Salmonella enterica serovar Typhimurium must successfully transition the broad fluctuations in oxygen concentrations encountered in the host. In Escherichia coli , FNR is one of the main regulatory proteins involved in O 2 sensing. To assess the role of FNR in serovar Typhimurium, we constructed an isogenic fnr mutant in the virulent wild-type strain (ATCC 14028s) and compared their transcriptional profiles and pathogenicities in mice. Here, we report that, under anaerobic conditions, 311 genes (6.80% of the genome) are regulated directly or indirectly by FNR; of these, 87 genes (28%) are poorly characterized. Regulation by FNR in serovar Typhimurium is similar to, but distinct from, that in E. coli. Thus, genes/operons involved in aerobic metabolism, NO· detoxification, flagellar biosynthesis, motility, chemotaxis, and anaerobic carbon utilization are regulated by FNR in a fashion similar to that in E. coli . However, genes/operons existing in E. coli but regulated by FNR only in serovar Typhimurium include those coding for ethanolamine utilization, a universal stress protein, a ferritin-like protein, and a phosphotransacetylase. Interestingly, Salmonella -specific genes/operons regulated by FNR include numerous virulence genes within Salmonella pathogenicity island 1 (SPI-1), newly identified flagellar genes ( mcpAC , cheV ), and the virulence operon ( srfABC ). Furthermore, the role of FNR as a positive regulator of motility, flagellar biosynthesis, and pathogenesis was confirmed by showing that the mutant is nonmotile, lacks flagella, is attenuated in mice, and does not survive inside macrophages. The inability of the mutant to survive inside macrophages is likely due to its sensitivity to the reactive oxygen species generated by NADPH phagocyte oxidase.}, number={6}, journal={JOURNAL OF BACTERIOLOGY}, author={Fink, Ryan C. and Evans, Matthew R. and Porwollik, Steffen and Vazquez-Torres, Andres and Jones-Carson, Jessica and Troxell, Bryan and Libby, Stephen J. and McClelland, Michael and Hassan, Hosni M.}, year={2007}, month={Mar}, pages={2262–2273} }
 @article{azcarate-peril_bruno-barcena_hassan_klaenhammer_2006, title={Transcriptional and functional analysis of oxalyl-coenzyme A (CoA) decarboxylase and formyl-CoA transferase genes from Lactobacillus acidophilus}, volume={72}, ISSN={["1098-5336"]}, url={http://europepmc.org/abstract/med/16517636}, DOI={10.1128/AEM.72.3.1891-1899.2006}, abstractNote={ABSTRACT Oxalic acid is found in dietary sources (such as coffee, tea, and chocolate) or is produced by the intestinal microflora from metabolic precursors, like ascorbic acid. In the human intestine, oxalate may combine with calcium, sodium, magnesium, or potassium to form less soluble salts, which can cause pathological disorders such as hyperoxaluria, urolithiasis, and renal failure in humans. In this study, an operon containing genes homologous to a formyl coenzyme A transferase gene ( frc ) and an oxalyl coenzyme A decarboxylase gene ( oxc ) was identified in the genome of the probiotic bacterium Lactobacillus acidophilus . Physiological analysis of a mutant harboring a deleted version of the frc gene confirmed that frc expression specifically improves survival in the presence of oxalic acid at pH 3.5 compared with the survival of the wild-type strain. Moreover, the frc mutant was unable to degrade oxalate. These genes, which have not previously been described in lactobacilli, appear to be responsible for oxalate degradation in this organism. Transcriptional analysis using cDNA microarrays and reverse transcription-quantitative PCR revealed that mildly acidic conditions were a prerequisite for frc and oxc transcription. As a consequence, oxalate-dependent induction of these genes occurred only in cells first adapted to subinhibitory concentrations of oxalate and then exposed to pH 5.5. Where genome information was available, other lactic acid bacteria were screened for frc and oxc genes. With the exception of Lactobacillus gasseri and Bifidobacterium lactis , none of the other strains harbored genes for oxalate utilization.}, number={3}, journal={APPLIED AND ENVIRONMENTAL MICROBIOLOGY}, author={Azcarate-Peril, MA and Bruno-Barcena, JM and Hassan, HM and Klaenhammer, TR}, year={2006}, month={Mar}, pages={1891–1899} }
 @article{bruno-barcena_azcarate-peril_klaenhammer_hassan_2005, title={Marker-free chromosomal integration of the manganese superoxide dismutase gene (sodA) from Streptococcus thermophilus into Lactobacillus gasseri}, volume={246}, ISSN={["1574-6968"]}, url={http://europepmc.org/abstract/med/15869967}, DOI={10.1016/j.femsle.2005.03.044}, abstractNote={A strategy for functional gene replacement in the chromosome of Lactobacillus gasseri is described. The phospho-β-galactosidase II gene (lacII) was functionally replaced by the manganese superoxide dismutase (MnSOD) gene (sodA) from Streptococcus thermophilus, by adapting the insertional inactivation method described for lactobacilli [Russell, W.M. and Klaenhammer, T.R. 2001 Efficient system for directed integration into the Lactobacillus acidophilus and Lactobacillus gasseri chromosomes via homologous recombination. Appl. Environ. Microbiol. 67, 4361–4364]. L. gasseri carrying the heterologous sodA gene grew on lactose as efficiently as the wild-type parent. An active MnSOD was expressed in the transgenic strain, and the enzyme migrated on PAGE-SOD activity gels to the same position as that of MnSOD from S. thermophilus. The expression of MnSOD from a single copy of sodA integrated in the chromosome of L. gasseri provided enhanced tolerance to hydrogen peroxide, and extended the viability of carbon/energy starved cultures stored at 25 °C. This is the first report showing the successful utilization of the pORI plasmids system to generate marker-free gene integration in L. gasseri strains.}, number={1}, journal={FEMS MICROBIOLOGY LETTERS}, author={Bruno-Barcena, JM and Azcarate-Peril, MA and Klaenhammer, TR and Hassan, HM}, year={2005}, month={May}, pages={91–101} }
 @article{bruno-barcena_andrus_libby_klaenhammer_hassan_2004, title={Expression of a heterologous manganese superoxide dismutase gene in intestinal lactobacilli provides protection against hydrogen peroxide toxicity}, volume={70}, ISSN={["1098-5336"]}, url={http://europepmc.org/abstract/med/15294805}, DOI={10.1128/AEM.70.8.4702-4710.2004}, abstractNote={ABSTRACT In living organisms, exposure to oxygen provokes oxidative stress. A widespread mechanism for protection against oxidative stress is provided by the antioxidant enzymes: superoxide dismutases (SODs) and hydroperoxidases. Generally, these enzymes are not present in Lactobacillus spp. In this study, we examined the potential advantages of providing a heterologous SOD to some of the intestinal lactobacilli. Thus, the gene encoding the manganese-containing SOD ( sodA ) was cloned from Streptococcus thermophilus AO54 and expressed in four intestinal lactobacilli. A 1.2-kb PCR product containing the sodA gene was cloned into the shuttle vector pTRK563, to yield pSodA, which was functionally expressed and complemented an Escherichia coli strain deficient in Mn and FeSODs. The plasmid, pSodA, was subsequently introduced and expressed in Lactobacillus gasseri NCK334, Lactobacillus johnsonii NCK89 , Lactobacillus acidophilus NCK56, and Lactobacillus reuteri NCK932. Molecular and biochemical analyses confirmed the presence of the gene ( sodA ) and the expression of an active gene product (MnSOD) in these strains of lactobacilli. The specific activities of MnSOD were 6.7, 3.8, 5.8, and 60.7 U/mg of protein for L. gasseri , L. johnsonii , L. acidophilus , and L. reuteri , respectively. The expression of S. thermophilus MnSOD in L. gasseri and L. acidophilus provided protection against hydrogen peroxide stress. The data show that MnSOD protects cells against hydrogen peroxide by removing O 2 ·− and preventing the redox cycling of iron. To our best knowledge, this is the first report of a sodA from S. thermophilus being expressed in other lactic acid bacteria.}, number={8}, journal={APPLIED AND ENVIRONMENTAL MICROBIOLOGY}, author={Bruno-Barcena, JM and Andrus, JM and Libby, SL and Klaenhammer, TR and Hassan, HM}, year={2004}, month={Aug}, pages={4702–4710} }
 @article{kong_bates_hulsmann_hassan_smith_oliver_2004, title={Role of catalase and oxyR in the viable but nonculturable state of Vibrio vulnificus}, volume={50}, ISSN={["1574-6941"]}, DOI={10.1016/j.femsec.2004.06.004}, abstractNote={Vibrio vulnificus has proven difficult to culture from water or shellfish during winter months, which is attributed to the viable but nonculturable (VBNC) state. Because reactive oxygen species were found to be involved in the low temperature-induced entrance of V. vulnificus into this state, we generated an oxyR mutant which lacks catalase activity. This strain is nonculturable on solid media even at ambient temperature, due to the presence of H2O2 in such media. Low temperature incubation of the parent resulted in loss of catalase activity, making the cells H2O2 sensitive, and paralleling the loss of culturability (entry into the VBNC state). Thus, cells of V. vulnificus in the VBNC state are likely exhibiting this response to low in situ temperature and only when the artificial condition of laboratory culture is attempted are the cells nonculturable due to cold-induced loss of catalase activity. To our knowledge, this is the first study providing direct evidence for the metabolic basis of nonculturability and the viable but nonculturable state.}, number={3}, journal={FEMS MICROBIOLOGY ECOLOGY}, author={Kong, IS and Bates, TC and Hulsmann, A and Hassan, H and Smith, BE and Oliver, JD}, year={2004}, month={Nov}, pages={133–142} }
 @article{passos_fleming_hassan_mcfeeters_2003, title={Effect of malic acid on the growth kinetics of Lactobacillus plantarum}, volume={63}, ISSN={["0175-7598"]}, DOI={10.1007/s00253-003-1375-7}, number={2}, journal={APPLIED MICROBIOLOGY AND BIOTECHNOLOGY}, author={Passos, FV and Fleming, HP and Hassan, HM and McFeeters, RF}, year={2003}, month={Dec}, pages={207–211} }
 @article{andrus_bowen_klaenhammer_hassan_2003, title={Molecular characterization and functional analysis of the manganese-containing superoxide dismutase gene (sodA) from Streptococcus thermophilus AO54}, volume={420}, ISSN={["1096-0384"]}, DOI={10.1016/j.abb.2003.09.007}, abstractNote={This report describes the isolation, sequencing, and functional analysis of the sodA gene, encoding Mn-superoxide dismutase, from Streptococcus thermophilus AO54. The gene was found to encode a 201 amino acid polypeptide with 88 and 83% identity to SodA from Streptococcus mutans and Streptococcus agalacticae, respectively. Primer extension analysis revealed a transcriptional start site 27 nucleotides upstream of initiation codon. The gene was expressed in Escherichia coli and was able to rescue the growth of a sodAsodB mutant in a minimal-medium containing 10(-6)M paraquat. A sodA mutant of S. thermophilus was constructed and found to be more sensitive to aerobic growth than its parent strain. Supplementing the medium with MnCl(2) improved the growth of the mutant, only under microaerophilic conditions. The results suggest that sodA is essential for the aerobic growth of S. thermophilus. In the absence of functional SodA, manganese ions may provide partial protection against oxygen toxicity.}, number={1}, journal={ARCHIVES OF BIOCHEMISTRY AND BIOPHYSICS}, author={Andrus, JM and Bowen, SW and Klaenhammer, TR and Hassan, HM}, year={2003}, month={Dec}, pages={103–113} }
 @article{hulsmann_rosche_kong_hassan_beam_oliver_2003, title={RpoS-dependent stress response and exoenzyme production in Vibrio vulnificus}, volume={69}, ISSN={["1098-5336"]}, DOI={10.1128/AEM.69.10.6114-6120.2003}, abstractNote={ABSTRACT Vibrio vulnificus is an estuarine bacterium capable of causing rapidly fatal infections through both ingestion and wound infection. Like other opportunistic pathogens, V. vulnificus must adapt to potentially stressful environmental changes while living freely in seawater, upon colonization of the oyster gut, and upon infection of such diverse hosts as humans and eels. In order to begin to understand the ability of V. vulnificus to respond to such stresses, we examined the role of the alternate sigma factor RpoS, which is important in stress response and virulence in many pathogens. An rpoS mutant of V. vulnificus strain C7184o was constructed by homologous recombination. The mutant strain exhibited a decreased ability to survive diverse environmental stresses, including exposure to hydrogen peroxide, hyperosmolarity, and acidic conditions. The most striking difference was a high sensitivity of the mutant to hydrogen peroxide. Albuminase, caseinase, and elastase activity were detected in the wild type but not in the mutant strain, and an additional two hydrolytic activities (collagenase and gelatinase) were reduced in the mutant strain compared to the wild type. Additionally, the motility of the rpoS mutant was severely diminished. Overall, these studies suggest that rpoS in V. vulnificus is important for adaptation to environmental changes and may have a role in virulence.}, number={10}, journal={APPLIED AND ENVIRONMENTAL MICROBIOLOGY}, author={Hulsmann, A and Rosche, TM and Kong, IS and Hassan, HM and Beam, DM and Oliver, JD}, year={2003}, month={Oct}, pages={6114–6120} }
 @article{caldwell_hassan_2002, title={Azotobacter chroococcum does not contain sodA or its gene product Mn-superoxide dismutase}, volume={48}, ISSN={["1480-3275"]}, DOI={10.1139/W02-003}, abstractNote={Azotobacter chroococcum and Azotobacter vinelandii grown in Burk medium with 1% mannitol (BM) or in BM supplemented with 2.2 mg/mL ammonium acetate (BM+N) were found to have only iron-containing and CuZn-containing superoxide dismutase. Furthermore, genomic DNA from A. chroococcum and A. vinelandii were subjected to polymerase chain reaction analysis using sodA- and sodB-specific primers and yielded only a sodB product. These results dispute the assertion by Buchanan and Lees (Can. J. Microbiol. 26: 441-447, 1980) that A. chroococcum contains Mn-superoxide dismutase.}, number={2}, journal={Canadian Journal of Microbiology}, author={Caldwell, J. and Hassan, H.M.}, year={2002}, month={Feb}, pages={183–187} }
 @article{qurollo_bishop_hassan_2001, title={Characterization of the iron superoxide dismutase gene of <i>Azotobacter vinelandii</i>: <i>sodB</i> may be essential for viability}, volume={47}, ISSN={1480-3275 0008-4166}, url={http://dx.doi.org/10.1139/cjm-47-1-63}, DOI={10.1139/cjm-47-1-63}, number={1}, journal={Canadian Journal of Microbiology}, publisher={Canadian Science Publishing}, author={Qurollo, Barbara A. and Bishop, Paul E. and Hassan, Hosni M.}, year={2001}, pages={63–71} }
 @misc{hassan_2001, title={Oxygen Radical Toxicity}, author={Hassan, H.}, year={2001}, month={May} }
 @article{lee_lee_kim_choi_hassan_chung_1998, title={Mechanism of regulation of 8-hydroxyguanine endonuclease by oxidative stress: Roles of fnr, arcA, and fur}, volume={24}, ISSN={["1873-4596"]}, DOI={10.1016/S0891-5849(97)00427-9}, abstractNote={We found previously that 8-hydroxyguanine (oh8Gua) endonuclease in E. coli is induced in response to oxidative stress in a fashion similar to the oxidative response of the Mn-superoxide dismutase (MnSOD). In this study, attempts were made to identify the genes involved in the co-regulation of E. coli endonuclease and MnSOD (sodA). oh8Gua nuclease is induced by molecular oxygen and a superoxide radical generator (paraquat) but not by H2O2, suggesting that the regulation of this endonuclease is dependent on SoxRS but independent of OxyR. This enzyme was induced by paraquat in all of the soxRS mutant strains used (soxR−, soxS− and soxRc), whereas glucose-6-phosphate dehydrogenase (a member of the soxRS regulon) showed the expected responses; therefore, this possibility was excluded. The presence of metal chelators in the growth medium caused the induction of this enzyme, and this induction was suppressed by the addition of Fe++. Consistent with this finding, this enzyme was expressed under anaerobiosis in all of the mutant strains of fnr in particular, as well as fur, arcA, and combinations thereof. These findings suggest that the oxidative regulation of oh8Gua endonuclease is under control of fnr, fur, and arcA, where fnr plays a predominant role. The multiple involvement of regulatory genes as well as co-regulation with antioxidant enzyme will enhance the efficiency of cellular growth and survival in the aerobic environment.}, number={7-8}, journal={FREE RADICAL BIOLOGY AND MEDICINE}, author={Lee, HS and Lee, YS and Kim, HS and Choi, JY and Hassan, HM and Chung, MH}, year={1998}, month={May}, pages={1193–1201} }
 @article{chang_hassan_1997, title={Characterization of superoxide dismutase in Streptococcus thermophilus}, volume={63}, number={9}, journal={Applied and Environmental Microbiology}, author={Chang, S. K. and Hassan, H. M.}, year={1997}, pages={3732–3735} }
 @inbook{hassan_1997, place={New York}, series={Lung Biology series}, title={Cytotoxicity of oxyradicals and the evolution of superoxide dismutases}, booktitle={Oxygen, gene expression and cellular function}, publisher={Marcel Dekker}, author={Hassan, H.M.}, editor={Massaro, D. and Clerch, L.Editors}, year={1997}, pages={26–51}, collection={Lung Biology series} }
 @article{sammour_hassan_1996, title={Enhancement of the antibacterial activity of ampicillin by liposome encapsulation}, volume={3}, ISSN={1071-7544 1521-0464}, url={http://dx.doi.org/10.3109/10717549609029460}, DOI={10.3109/10717549609029460}, abstractNote={This study showed that encapsulation of ampicillin (Amp) in liposomes prepared with synthetic lecithins enhanced its antibiotic activity against both Amp-sensitive and Amp-resistant Escherichia coli. This was demonstrated by growth inhibition of E. coli in the presence of the liposomal preparations containing Amp. Growth inhibition was also seen in the presence of exogenous β-lactamase. Adsorption of Amp onto the surface of the liposomes did not result in enhanced activity of the drug against E. coli. The encapsulation efficiency of Amp in liposomes prepared by the Bangham method (BM) was greatly affected by the phospholipids used. The efficiency increased with a rise in the phase transition temperature (Tc) of the phospholipid, the maximum encapsulation of Amp being obtained with distearoylphosphatidylcholine (DSPC). The entrapment efficiency of Amp with the reverse phase evaporation method (REV) was largely superior to that with the BM method. Kinetic studies using DSPC liposomes prepared by the REV and BM protocols demonstrated that Amp-loaded liposomes contained 60 and 72% of drug, respectively, after 24 h at 37°C.}, number={4}, journal={Drug Delivery}, publisher={Informa UK Limited}, author={Sammour, Omima A. and Hassan, Hosni M.}, year={1996}, month={Jan}, pages={273–278} }
 @article{presutti_hassan_1995, title={Binding of integration host factor (IHF) to the Escherichia coli sodA gene and its role in the regulation of a sodA-lacZ fusion gene}, volume={246}, ISSN={0026-8925 1432-1874}, url={http://dx.doi.org/10.1007/bf00294686}, DOI={10.1007/bf00294686}, number={2}, journal={Molecular and General Genetics MGG}, publisher={Springer Science and Business Media LLC}, author={Presutti, David G. and Hassan, Hosni M.}, year={1995}, month={Mar}, pages={228–235} }
 @misc{hassan_1995, title={Metals in Biology}, author={Hassan, H.M.}, year={1995} }
 @inbook{hassan_1994, place={NY}, title={Regulation of the biosynthesis of manganese-superoxide dismutase in Escherichia coli in response to iron and manganese}, booktitle={Frontiers of reactive oxygen species in biology and medicine}, publisher={Elsevier Science}, author={Hassan, H.M.}, editor={Asada, K. and Yoshikawa, T.Editors}, year={1994}, pages={245–250} }
 @article{hassan_schrum_1994, title={Roles of manganese and iron in the regulation of the biosynthesis of manganese-superoxide dismutase inEscherichia coli}, volume={14}, ISSN={0168-6445 1574-6976}, url={http://dx.doi.org/10.1111/j.1574-6976.1994.tb00105.x}, DOI={10.1111/j.1574-6976.1994.tb00105.x}, abstractNote={Aerobic life-style offers both benefits and risks to living cells. The major risk comes from the formation of reactive oxygen intermediates (i.e. superoxide radical, O2-; hydrogen peroxide, H2O2; and hydroxyl radical, OH.) during normal oxygen metabolism. However, living cells are able to cope with oxygen toxicity by virtue of a unique set of antioxidant enzymes that scavenge O2- and H2O2, and prevent the formation OH.. Superoxide dismutases (SODs; EC 1.15.1.1) are metalloenzymes essential for aerobic survival. Escherichia coli contains two forms of this enzyme: an iron-containing enzyme (FeSOD) and a manganese-containing enzyme (MnSOD). In E. coli, MnSOD biosynthesis is under rigorous control. The enzyme is induced in response to a variety of environmental stress conditions including exposure to oxygen, redox cycling compounds such as paraquat which exacerbate the level of intracellular superoxide radicals, iron chelation (i.e. iron deprivation), and oxidants. A model for the regulation of the MnSOD has been proposed in which the MnSOD gene (sodA) is negatively regulated at the level of transcription by an iron-containing redox-sensitive repressor protein. The effect of iron-chelation most probably results in removal of the iron necessary for repressor activity. Recent studies have shown that sodA expression is regulated by three iron-dependent regulatory proteins, Fur (ferric uptake regulation), Fnr (fumarate nitrate regulation) and SoxR (superoxide regulon), and by the ArcA/ArcB (aerobic respiration control) system. The potential Fur-, Fnr- and ArcA-binding sites in the sodA promoter region have been identified by using different cis-acting regulatory mutations that caused anaerobic derepression of the gene.(ABSTRACT TRUNCATED AT 250 WORDS)}, number={4}, journal={FEMS Microbiology Reviews}, publisher={Oxford University Press (OUP)}, author={Hassan, Hosni M. and Schrum, Laura W.}, year={1994}, month={Aug}, pages={315–323} }
 @article{schrum_hassan_1994, title={Stability of Escherichia coli sodA mRNA and identification of the transcriptional start site(s) under different environmental and oxidative stresses}, volume={17}, ISSN={0891-5849}, url={http://dx.doi.org/10.1016/0891-5849(94)90076-0}, DOI={10.1016/0891-5849(94)90076-0}, abstractNote={Manganese-containing superoxide dismutase (MnSOD- sodA ) in Escherichia coli (E. coli) is regulated at the transcriptional level as observed in studies using both operon and gene fusions. In this paper were examine the regulation of sodA gene at the level of mRNA. We examine the effects of several aerobic inducing conditions (i.e., nalidixic acid, paraquat, or 2,2′-dipyridyl) on mRNA stability, transcription initiation, and translation. The half-life of sodA mRNA was found to be approximately 3–4 min, showing no differences in mRNA stability between induced and uninduced cells. We also found, by reverse transcriptase, that the second putative promoter is not functional under normal or stress conditions, and the amount of mRNA was found to be proportional to active MnSOD. Thus, these results indicate that under oxidative stress/inducing conditions, the increase in aerobic transcription of sodA occurs from only one transcription start site without affecting the stability of sodA mRNA. In addition, the 1:1 ratio found between increases in sodA mRNA and active MnSOD suggests that no translational regulation occurs aerobically.}, number={3}, journal={Free Radical Biology and Medicine}, publisher={Elsevier BV}, author={Schrum, Laura W. and Hassan, Hosni M.}, year={1994}, month={Sep}, pages={209–213} }
 @article{schrum_hassan_1994, title={The Effects of fur on the Transcriptional and Post-transcriptional Regulation of MnSOD Gene (sodA) in Escherichia coli}, volume={309}, ISSN={0003-9861}, url={http://dx.doi.org/10.1006/abbi.1994.1115}, DOI={10.1006/abbi.1994.1115}, abstractNote={Earlier studies have shown that the Fur (ferric uptake regulation) protein acts as an anaerobic/aerobic repressor of MnSOD (sodA) expression. We found that the aerobic expression of sodA::lacZ fusion in a Fur− background to be threefold higher than in a Fur+ background. This effect of fur mutation was not seen in a strain harboring the sodA+ gene instead of the sodA::lacZ fusion. However, we observed a proportionate increase in the concentrations of sodA::lacZ and sodA+ mRNAs in response to a mutation in the fur gene. These data suggest that the formation of active MnSOD is dependent on a functional fur gene. Indeed, we found that in a fur mutant iron was incorporated into SodA in place of manganese, thus creating inactive and/or partially active forms of the enzyme (i.e., Fe2SodA and/or Mn,FeSodA, respectively), resulting in little or no increase in total MnSOD activity. Thus, Fur plays the role of a repressor at the transcriptional level, but it also plays an indirect role at the post-transcriptional level where it affects the maturation of SodA into a fully active enzyme, Mn2SodA (MnSOD).}, number={2}, journal={Archives of Biochemistry and Biophysics}, publisher={Elsevier BV}, author={Schrum, L.W. and Hassan, H.M.}, year={1994}, month={Mar}, pages={288–292} }
 @article{bowen_hassan_1993, title={Characterization of cis-Acting Regulatory Mutations Causing Anaerobic Expression of the sodA Gene in Escherichia coli}, volume={302}, ISSN={0003-9861}, url={http://dx.doi.org/10.1006/abbi.1993.1226}, DOI={10.1006/abbi.1993.1226}, abstractNote={The biosynthesis of Mn-containing superoxide dismutase is regulated in response to stimuli that affect the redox potential of the cell. To further investigate the mode of regulation of the gene (sodA) encoding this enzyme, cis-acting regulatory mutations in a strain containing a sodA::lacZ gene fusion were studied. The mutant strains expressed β-galactosidase under anaerobic conditions, whereas the wild-type did not. Furthermore, the mutants were not induced in response to the presence of iron chelator, 2,2′-dipyridyl, or to the redox cycling compound, paraquat. The wild-type, however, did respond to these effectors. In vivo cloning was used to isolate the cis-acting regulatory elements from the mutants (NC4 and NC5). Replacement of the wild-type 5′-regulatory region with either of the mutants′ cis-acting regulatory element resulted in the anaerobic expression of active Mn-superoxide dismutase. Sequence and restriction analysis revealed the presence of an IS2 insertion element in the promoter region of one of the mutants (NC5). This insertion caused the displacement of the 5′-regulatory region of sodA and the formation of a functional hybrid promoter consisting of the resident −10 region from sodA and −35 from IS2. The second mutation (from NC4) was similarly analyzed, and an IS5 element was identified. The insertion site of IS5 (in NC4) was 6 bp (5′-TTAATT-3′) upstream from the IS2 site (in NC5). Anaerobic expression of sodA in NC4 was lower than in NC5. This difference was almost eliminated in an arc− background, suggesting that the sequence 5′-TTAATT-3′ might be essential for negative regulation by ArcA.}, number={2}, journal={Archives of Biochemistry and Biophysics}, publisher={Elsevier BV}, author={Bowen, S.W. and Hassan, H.M.}, year={1993}, month={May}, pages={372–379} }
 @article{beaumont_hassan_1993, title={Characterization of regulatory mutations causing anaerobic derepression of the sodA gene in Escherichia coli K12: cooperation between cis- and trans-acting regulatory loci}, volume={139}, ISSN={0022-1287}, url={http://dx.doi.org/10.1099/00221287-139-11-2677}, DOI={10.1099/00221287-139-11-2677}, abstractNote={The genetic loci leading to anaerobic derepression of a sodA::lacZ protein fusion in a UV-generated mutant strain (UV14) of Escherichia coli were identified. The mutant (UV14) was found to harbour two altered loci: one is in the trans-regulatory gene fnr (fumarate nitrate reduction) where leucine-129 was changed to glutamine (fnr14), and the second (sodA14) is in the promoter region (cis) of the sodA gene apparently affecting the binding of the Fur (ferric uptake regulation) protein. Introduction of an fnr+ gene into UV14 restored anaerobic repression of sodA::lacZ and restored the ability of the cells to reduce nitrate. However, when either the fnr14 or the sodA14 mutation was introduced into an otherwise wild-type background, only slight anaerobic derepression of sodA was observed. When both the cis- and trans-acting mutations (i.e. sodA14 and fnr14) were combined simultaneously in an otherwise wild-type background, the specific activity of sodA::lacZ expression was comparable to that of the original mutant strain (UV14). Furthermore, a genetically confirmed fur fnr double mutant was also similarly derepressed in anaerobic sodA::lacZ expression. The data presented suggest that the cis-mutation in UV14 (sodA14) affects the Fur-binding site in the sodA promoter, while having no effect on Fnr or Arc mediated repression. Also, a second putative Fnr-binding site that straddles the ribosomal binding-site was identified in the sodA gene.}, number={11}, journal={Journal of General Microbiology}, publisher={Microbiology Society}, author={Beaumont, M. D. and Hassan, H. M.}, year={1993}, month={Nov}, pages={2677–2684} }
 @article{roy_klaenhammer_hassan_1993, title={Cloning and expression of the manganese superoxide dismutase gene of Escherichia coli in Lactococcus lactis and Lactobacillus gasseri}, volume={239}, ISSN={0026-8925 1432-1874}, url={http://dx.doi.org/10.1007/bf00281598}, DOI={10.1007/bf00281598}, number={1-2}, journal={Molecular and General Genetics MGG}, publisher={Springer Science and Business Media LLC}, author={Roy, Dipika G. and Klaenhammer, Todd R. and Hassan, Hosni M.}, year={1993}, month={May}, pages={33–40} }
 @article{passos_ollis_fleming_hassan_felder_1993, title={Modeling the cucumber fermentation: Growth ofLactobacillus plantarum}, volume={12}, ISSN={0169-4146 1476-5535}, url={http://dx.doi.org/10.1007/bf01584212}, DOI={10.1007/bf01584212}, abstractNote={Specific growth rate models of product-inhibited cell growth exist but are rarely applied to fermentations beyond ethanol and large-scale antibiotic production. The present paper summarizes experimental data and the development of a model for growth of the commercially important bacterium,Lactobacillus plantarum, in cucumber juice. The model provides an excellent correlation of data for the influence on bacterial growth rate of NaCl, protons (H+), and the neutral, inhibitory forms of acetic acid and the fermentation product, lactic acid. The effects of each of the variables are first modeled separately using established functional forms and then combined in the final model formulation.}, number={3-5}, journal={Journal of Industrial Microbiology}, publisher={Oxford University Press (OUP)}, author={Passos, F. V. and Ollis, D. F. and Fleming, H. P. and Hassan, H. M. and Felder, R. M.}, year={1993}, month={Sep}, pages={341–345} }
 @article{passos_fleming_ollis_hassan_felder_1993, title={Modeling the specific growth rate of Lactobacillus plantarum in cucumber extract}, volume={40}, ISSN={0175-7598 1432-0614}, url={http://dx.doi.org/10.1007/bf00170443}, DOI={10.1007/bf00170443}, number={1}, journal={Applied Microbiology and Biotechnology}, publisher={Springer Science and Business Media LLC}, author={Passos, F.V. and Fleming, H.P. and Ollis, D.F. and Hassan, H.M. and Felder, R.M.}, year={1993}, month={Oct} }
 @article{schrum_hassan_1993, title={Transcriptional activation of Mn-superoxide dismutase gene (sodA) of Escherichia coli by MnCl2}, volume={1216}, ISSN={0167-4781}, url={http://dx.doi.org/10.1016/0167-4781(93)90143-2}, DOI={10.1016/0167-4781(93)90143-2}, abstractNote={Transcription of the manganese-superoxide dismutase gene ( sodA ) in Escherichia coli was shown to be activated by manganese. Addition of MnCl 2 increased the expression of β-galactosidase from a sodA::lacZ protein fusion and increased the concentration of mRNA transcribed from sodA + and sodA::lacZ constructs. The stimulatory affect of manganese on the expression of sodA::lacZ was greatly reduced (i.e., > 90%) in a strain harboring a fur mutation. We also found that manganese was capable of altering DNA topology. These results show that Mn 2+ causes activation of sodA transcription.}, number={2}, journal={Biochimica et Biophysica Acta (BBA) - Gene Structure and Expression}, publisher={Elsevier BV}, author={Schrum, Laura W. and Hassan, Hosni M.}, year={1993}, month={Nov}, pages={186–190} }
 @article{beaumont_hassan_1992, title={Characterization oftrans-acting regulatory elements affecting the expression of Mn-superoxide dismutase (sodA) inEscherichia coli}, volume={25}, ISSN={0343-8651 1432-0991}, url={http://dx.doi.org/10.1007/bf01571021}, DOI={10.1007/bf01571021}, number={3}, journal={Current Microbiology}, publisher={Springer Science and Business Media LLC}, author={Beaumont, Mark D. and Hassan, Hosni M.}, year={1992}, month={Sep}, pages={135–141} }
 @article{rivers_hassan_1992, title={Isolation and characterization of an Escherichia coli mutant elevated in manganese-containing superoxide dismutase biosynthesis}, volume={11}, journal={Biochem. (Life Sci. Adv.)}, author={Rivers, J.C. and Hassan, H.M.}, year={1992}, pages={23–30} }
 @article{hassan_sun_1992, title={Regulatory roles of Fnr, Fur, and Arc in expression of manganese-containing superoxide dismutase in Escherichia coli.}, volume={89}, ISSN={0027-8424 1091-6490}, url={http://dx.doi.org/10.1073/pnas.89.8.3217}, DOI={10.1073/pnas.89.8.3217}, abstractNote={Transcriptional regulation of the sodA gene, encoding the manganese superoxide dismutase (superoxide: superoxide oxidoreductase, EC 1.15.1.1) of Escherichia coli, was studied by monitoring expression of sodA-lacZ in different genetic backgrounds and under different growth conditions. Mutations in the fnr gene were found to affect aerobic and anaerobic expression of sodA-lacZ. Potential Fnr-binding sites were identified in the promoter region of sodA. Strains harboring simultaneous mutations in arcA/B and fur expressed sodA-lacZ under anaerobic growth conditions but were still inducible by iron chelators. However, in the triple mutants (fnr fur arcA/B) sodA-lacZ was fully expressed under anaerobiosis and was not further induced by the presence of 2,2'-dipyridyl, nitrate, or oxidants. On the other hand, aerobic expression of sodA-lacZ from a Fur-strain was approximately 3.8-fold higher than that from the wild-type strain but was diminished by introducing mutations in fnr or arcA/B. In conclusion, Fnr, Arc, and Fur act as anaerobic repressors of sodA. Furthermore, the regulation of sodA by Fur (ferric uptake regulation protein), Arc (aerobic respiratory control), and Fnr (fumarate nitrate reduction/regulator of anaerobic respiration) is independent of the superoxide response regulon SoxRS.}, number={8}, journal={Proceedings of the National Academy of Sciences}, publisher={Proceedings of the National Academy of Sciences}, author={Hassan, H. M. and Sun, H. C.}, year={1992}, month={Apr}, pages={3217–3221} }
 @article{schrum_hassan_1992, title={Transcriptional regulation of Mn-superoxide dismutase gene (sodA) of Escherichia coli is stimulated by DNA gyrase inhibitors}, volume={299}, ISSN={0003-9861}, url={http://dx.doi.org/10.1016/0003-9861(92)90261-t}, DOI={10.1016/0003-9861(92)90261-t}, abstractNote={The expression of manganese-containing superoxide dismutase (sodA) in Escherichia coli using sodA::lacZ gene fusion was found to be stimulated by DNA gyrase inhibitors, nalidixic acid, or coumermycin A1. Aerobically, the gyrase inhibitors increased the expression of sodA::lacZ in the presence or absence of either paraquat or the iron chelator 2,2'-dipyridyl. The concentrations of the inhibitors used were found to reduce DNA supercoiling. Treatment of wild-type cells (sodA+) with nalidixic acid increased the transcription of MnSOD mRNA. Anaerobically, the expression of sodA::lacZ in wild-type cells was not affected by nalidixic acid. However, nalidixic acid had a stimulatory effect on the anaerobic expression of sodA::lacZ in cells preinduced by the iron chelator as well as in mutants derepressed in sodA expression by virtue of their lacking the trans-acting repressor proteins or the cis-acting regulatory elements needed for sodA regulation. The results indicate that the effect of DNA gyrase inhibitors is secondary to the cis- and trans-regulatory elements of sodA and suggest that changes in DNA topology may affect transcriptional regulation of sodA.}, number={1}, journal={Archives of Biochemistry and Biophysics}, publisher={Elsevier BV}, author={Schrum, Laura W. and Hassan, Hosni M.}, year={1992}, month={Nov}, pages={185–192} }
 @inbook{hassan_schiavone_1991, place={NY}, title={The role of oxygen free radicals in biology and evolution}, ISBN={0412333600; 9780412333606}, booktitle={Metazoan Life Without Oxygen}, publisher={Chapman and Hall}, author={Hassan, H.M. and Schiavone, J.R.}, editor={Bryant, C.Editor}, year={1991}, pages={19–37} }
 @article{mcdonald_hassan_fleming_daeschel_1991, title={Use of continuous culture for internal pH determination of lactic acid bacteria}, volume={8}, ISSN={0740-0020}, url={http://dx.doi.org/10.1016/0740-0020(91)90006-n}, DOI={10.1016/0740-0020(91)90006-n}, abstractNote={The response of cytoplasmic pH to external cellular pH was shown to be influenced by the growth phase forLeuconostoc mesenteroides, but not forLactobacillus plantarum. A continuous culture system was shown to reduce growth phase effects, and offer the advantage of more consistency in internal pH values. Oxygen, manganese, cell density, external pH, and organic acid production were shown not to influence the internal pH of these bacteria when grown in continuous culture.}, number={2}, journal={Food Microbiology}, publisher={Elsevier BV}, author={McDonald, L.C. and Hassan, H.M. and Fleming, H.P. and Daeschel, M.A.}, year={1991}, month={Jun}, pages={137–142} }
 @article{mcdonald_fleming_hassan_1990, title={Acid Tolerance of
            Leuconostoc mesenteroides
            and
            Lactobacillus plantarum}, volume={56}, ISSN={0099-2240 1098-5336}, url={http://dx.doi.org/10.1128/aem.56.7.2120-2124.1990}, DOI={10.1128/aem.56.7.2120-2124.1990}, abstractNote={In this study, we determined the internal cellular pH response of Leuconostoc mesenteroides and Lactobacillus plantarum to the external pH created by the microorganisms themselves or by lactic or acetic acids and their salts added to the growth medium. Growth of Leuconostoc mesenteroides stopped when its internal pH reached 5.4 to 5.7, and growth of L. plantarum stopped when its internal pH reached 4.6 to 4.8. Variation in growth medium composition or pH did not alter the growth-limiting internal pH reached by these microorganisms. L. plantarum maintained its pH gradient in the presence of either 160 mM sodium acetate or sodium lactate down to an external pH of 3.0 with either acid. In contrast, the ΔpH of Leuconostoc mesenteroides was zero at pH 4.0 with acetate and 5.0 with lactate. No differences were found between d -(−)- and l -(+)-lactic acid for the limiting internal pH for growth of either microorganism. The comparatively low growth-limiting internal pH and ability to maintain a pH gradient at high organic acid concentration may contribute to the ability of L. plantarum to terminate vegetable fermentations.}, number={7}, journal={Applied and Environmental Microbiology}, publisher={American Society for Microbiology}, author={McDonald, L. C. and Fleming, H. P. and Hassan, H. M.}, year={1990}, month={Jul}, pages={2120–2124} }
 @inbook{hassan_scandalios_1990, place={NY}, series={Plant Biology}, title={Superoxide dismutases in aerobic organisms}, ISBN={0471568104; 9780471568100}, booktitle={Stress Responses in Plants: Adaptation and Acclimation Mechanisms}, publisher={Wiley-Liss}, author={Hassan, H.M. and Scandalios, J.G.}, editor={Alscher, R.G. and Cumming, J.R.Editors}, year={1990}, pages={175–199}, collection={Plant Biology} }
 @article{naik_hassan_1990, title={Use of site-directed mutagenesis to identify an upstream regulatory sequence of sodA gene of Escherichia coli K-12.}, volume={87}, ISSN={0027-8424 1091-6490}, url={http://dx.doi.org/10.1073/pnas.87.7.2618}, DOI={10.1073/pnas.87.7.2618}, abstractNote={Mn-containing superoxide dismutase (SodA; superoxide:superoxide oxidoreductase, EC 1.15.1.1) biosynthesis in Escherichia coli is regulated by several environmental stimuli. The DNA sequence of sodA shows the presence of a potential binding site for a regulatory protein(s) at the -35 region. To explore the possible role of this region in the regulation of sodA, we used oligonucleotide-directed site-specific mutagenesis to change the sequence of nucleotides -48 through -44 from 5'-GGCAT-3' to 5'-TTACG-3'. We studied the effect of this altered sequence on the expression of sodA. The data showed that the altered sequence resulted in the constitutive expression of the gene. Thus, E. coli harboring a plasmid containing the mutated sodA gene (pSNM6) were uninducible by paraquat in aerobiosis or by 2,2'-dipyridyl in aerobiosis or anaerobiosis. Furthermore, a multicopy plasmid containing the mutated sodA failed to titrate the repressor molecules present in an E. coli strain carrying the sodA-lacZ fusion. In contrast, multicopy plasmids containing the wild-type sodA gene were able to titrate the repressor protein and to cause the anaerobic induction of beta-galactosidase in this sodA-lacZ fusion strain. These results indicate that the region within and around the mutated sequence probably plays an important role in sodA regulation and that the mutation disrupts a sequence that interacts with the repressor.}, number={7}, journal={Proceedings of the National Academy of Sciences}, publisher={Proceedings of the National Academy of Sciences}, author={Naik, S. M. and Hassan, H. M.}, year={1990}, month={Apr}, pages={2618–2622} }
 @article{schellhorn_pou_moody_hassan_1989, title={An electron spin resonance study of oxyradical generation in superoxide dismutase- and catalase-deficient mutants of Escherichia coli K-12}, volume={271}, ISSN={0003-9861}, url={http://dx.doi.org/10.1016/0003-9861(89)90282-8}, DOI={10.1016/0003-9861(89)90282-8}, abstractNote={The response of superoxide dismuase- and catalase-deficient strains of Escherichia coli to redox active compounds was examined by electron spin resonance. Levels of radicals formed in response to pyocyanine in situ were extremely low and were found to be predominantly extracellular, even in a strain completely deficient in both superoxide dismutase and catalase. In cell-free extracts of superoxide dismutase-minus strains incubated with NADPH and pyocyanine, the primary accumulating radical was the superoxide anion (O2−), although low levels of the hydroxyl radical (.OH) were also detected. In contrast, extracts from strains lacking catalase were found to accumulate higher levels of hydroxyl radicals.}, number={2}, journal={Archives of Biochemistry and Biophysics}, publisher={Elsevier BV}, author={Schellhorn, Herb E. and Pou, Sovitj and Moody, Carmella and Hassan, Hosni M.}, year={1989}, month={Jun}, pages={323–331} }
 @inbook{hassan_1989, place={Basel, Switzerland}, series={Forum of Nutrition}, title={Attenuation of Antioxidant Enzymes in Response to Oxidative Stresses1}, ISBN={9783805548489 9783318036015}, ISSN={1660-0347 1662-2987}, url={http://dx.doi.org/10.1159/000416712}, DOI={10.1159/000416712}, booktitle={Nutritional Impact of Food Processing. 25th Symposium of the Group of European Nutritionists, Reykjavik, September 1987}, publisher={S. Karger AG}, author={Hassan, Hosni M.}, editor={Somogyi, J.C. and Müller, H.R.Editors}, year={1989}, pages={278–287}, collection={Forum of Nutrition} }
 @article{hassan_lee_1989, title={Effect of temperature andhtpRon the biosynthesis of superoxide dismutase inEscherichia coli}, volume={58}, ISSN={0378-1097 1574-6968}, url={http://dx.doi.org/10.1111/j.1574-6968.1989.tb03033.x}, DOI={10.1111/j.1574-6968.1989.tb03033.x}, abstractNote={The synthesis of Mn- and FeSODs in response to temperature changes was examined in strains of Escherichia coli with different mutations in sod and htpR genes. Growth at or shift to elevated temperatures induced FeSOD but not MnSOD. The induction of FeSOD by heat was inhibited by chloramphenicol and was independent of the heat shock (htpR-controlled) regulon. FeSOD was more stable at 42 degrees C than was MnSOD.}, number={2-3}, journal={FEMS Microbiology Letters}, publisher={Oxford University Press (OUP)}, author={Hassan, Hosni M. and Lee, Fang-Jen S.}, year={1989}, month={Apr}, pages={133–137} }
 @inbook{hassan_1989, title={Microbial Superoxide Dismutases}, ISBN={9780120176267}, ISSN={0065-2660}, url={http://dx.doi.org/10.1016/s0065-2660(08)60223-0}, DOI={10.1016/s0065-2660(08)60223-0}, abstractNote={The presence of oxygen in the environment presents both advantages and threat to all forms of life. The use of oxygen as a final electron acceptor provides more energy than that afforded by anaerobic fermentation. Oxygen is also useful in many biosynthetic reactions. Superoxide radicals are normal and common by-products of aerobic existence. Superoxide dismutases are indispensable for protection against the toxicity of superoxide radicals. The evolution of three types of SODs to accomplish the same reaction in different organisms attests to their vital role in aerobic survival. Moreover, recent developments in the regulation of MnSODs, and the success in cloning FeSOD and MnSOD genes of E. coli, and the isolation of regulatory mutants can certainly open new research avenues to better understand the regulation of these enzymes. Finally, the knowledge gained from E. coli will make it possible to explore the regulation of SODs in other organisms. We look forward to active and exciting developments in SOD research.}, booktitle={Advances in Genetics}, publisher={Elsevier}, author={Hassan, Hosni M.}, year={1989}, pages={65–97} }
 @article{schiavone_hassan_1988, title={An assay for the detection of superoxide dismutase in individual Escherichia coli colonies}, volume={168}, ISSN={0003-2697}, url={http://dx.doi.org/10.1016/0003-2697(88)90343-0}, DOI={10.1016/0003-2697(88)90343-0}, abstractNote={A method for detecting superoxide dismutase activity in individual colonies of Escherichia coli was developed. The assay involves the lysis of individual cells in colonies on filter papers by a series of lysozyme, chloroform, and freeze-thaw treatments. Filters are placed on agar plates to allow diffusion of cellular enzymes into a solid matrix. A nitroblue tetrazolium overlay is applied to detect superoxide dismutase activity. Colonies possessing activity produce achromatic zones against a dark Formazan background. The assay can detect the presence of superoxide dismutase and the relative amount of enzyme as well. This assay provides a method for screening a population of cells for mutants deficient in or overproducing superoxide dismutase.}, number={2}, journal={Analytical Biochemistry}, publisher={Elsevier BV}, author={Schiavone, Joan R. and Hassan, Hosni M.}, year={1988}, month={Feb}, pages={455–461} }
 @article{andersson_daeschel_hassan_1988, title={Antibacterial activity of plantaricin SIK-83, a bacteriocin produced by Lactobacillus plantarum}, volume={70}, ISSN={0300-9084}, url={http://dx.doi.org/10.1016/0300-9084(88)90211-8}, DOI={10.1016/0300-9084(88)90211-8}, abstractNote={Lactobacillus plantarum SIK-83 produces a bacteriocin, designated plantaricin SIK-83, which inhibits 66 of 68 lactic acid bacteria from the genera Lactobacillus, Leuconostoc, Pediococcus and Streptococcus. A 500-fold dilution of L. plantarum SIK-83 MRS culture supernatant with phosphate buffer was sufficient to kill 105 cells/ml of Pediococcus pentosaceus within 120s. The killing of a sensitive population followed exponential kinetics. It shown that the bacteriocin binds specifically to sensitive cells but not to nonsensitive lactic acid bacteria, the producer strain or Gram-negative bacteria. Sensitive cells, after exposure to the bacteriocin, could be rescued by treatment with proteolytic enzymes. In buffer, plantaricin SIK-83 was adsorbed to the cell surface almost immediately, and morphological lesions were observed within 2 h after the cells were exposed to the bacteriocin. The lethal mode of action appeared to be due to damage to the cell membrane, resulting in cell lysis, which was detected by electron microscopy and by determination of released intracellular components.}, number={3}, journal={Biochimie}, publisher={Elsevier BV}, author={Andersson, Rolf E. and Daeschel, Mark A. and Hassan, Hosni M.}, year={1988}, month={Mar}, pages={381–390} }
 @article{bowen_hassan_1988, title={Induction of the manganese-containing superoxide dismutase in Escherichia coli is independent of the oxidative stress (oxyR-controlled) regulon.}, volume={263}, ISSN={0021-9258}, url={http://dx.doi.org/10.1016/s0021-9258(18)68110-4}, DOI={10.1016/s0021-9258(18)68110-4}, abstractNote={The synthesis of manganese-superoxide dismutase in response to hydrogen peroxide and to paraquat was examined in strains of Escherichia coli with different mutations in the oxyR gene. Hydrogen peroxide treatment did not induce manganese-superoxide dismutase, but did induce the oxyR regulon. Paraquat induced this enzyme in a strain compromised in its ability to induce the defense response against oxidative stress (oxyR deletion) as well as in a strain that is constitutive and overexpresses the oxyR regulon. Catalase (HPI), but not manganese-superoxide dismutase, was over-expressed under anaerobic conditions in a strain harboring a constitutive oxyR mutation. The data clearly demonstrate that the induction of manganese-superoxide dismutase is independent of the oxyR-controlled regulon.}, number={29}, journal={Journal of Biological Chemistry}, publisher={Elsevier BV}, author={Bowen, S W and Hassan, H M}, year={1988}, month={Oct}, pages={14808–14811} }
 @article{schellhorn_hassan_1988, title={Isolation and characterization of respiratory-deficient mutants of Escherichia coli K-12}, volume={170}, ISSN={0021-9193 1098-5530}, url={http://dx.doi.org/10.1128/jb.170.1.78-83.1988}, DOI={10.1128/jb.170.1.78-83.1988}, abstractNote={Several mutants of Escherichia coli K-12 defective in aerobic metabolism were isolated. One such mutant was found to be deficient in cytochromes, heme, and catalase. Aerobically grown cells did not consume oxygen and could grow only on fermentable carbon sources. Supplementation of the growth medium with delta-aminolevulonic acid, protoporphyrin IX, or hemin did not restore aerobic metabolism. The lack of heme and catalase in mutant cells grown on glucose was not due to catabolite repression, since the addition of exogenous cyclic AMP did not restore the normal phenotype. When grown aerobically on complex medium containing glucose, the mutant produced lactic acid as the principal fermentation product. This pleotropic mutation was attributed to an inability of the cells to synthesize heme, and preliminary data mapped the mutation to between 8 and 13 min on the E. coli genome.}, number={1}, journal={Journal of Bacteriology}, publisher={American Society for Microbiology}, author={Schellhorn, H E and Hassan, H M}, year={1988}, month={Jan}, pages={78–83} }
 @article{hassan_1988, title={Regulation and synthesis of superoxide dismutase}, volume={5}, journal={Free Radical Biology and Medicine}, author={Hassan, H.M.}, year={1988}, pages={377–385} }
 @article{schellhorn_hassan_1988, title={Response of hydroperoxidase and superoxide dismutase deficient mutants of Escherichia coli K-12 to oxidative stress}, volume={34}, ISSN={0008-4166 1480-3275}, url={http://dx.doi.org/10.1139/m88-206}, DOI={10.1139/m88-206}, abstractNote={In Escherichia coli, the coordinate action of two antioxidant enzymes, superoxide dismutase and hydroperoxidase (catalase), protect the cell from the deleterious effects of oxyradicals generated during normal aerobic respiration. To evaluate the relative importance of these two classes of enzymes, strains of E. coli deficient in superoxide dismutase and (or) hydroperoxidase were constructed by generalized transduction and their physiological responses to oxygen and oxidant stress examined. Superoxide dismutase was found to be more important than hydroperoxidase in preventing oxygen-dependent growth inhibition and mutagenesis, and in reducing sensitivity to redox-active compounds known to generate the superoxide anion. However, both types of enzymes were required for an effective defense against chemical oxidants that generate superoxide radicals and hydrogen peroxide.}, number={10}, journal={Canadian Journal of Microbiology}, publisher={Canadian Science Publishing}, author={Schellhorn, Herb E. and Hassan, Hosni M.}, year={1988}, month={Oct}, pages={1171–1176} }
 @article{whiteside_hassan_1988, title={Role of oxyradicals in the inactivation of catalase by ozone}, volume={5}, ISSN={0891-5849}, url={http://dx.doi.org/10.1016/0891-5849(88)90101-3}, DOI={10.1016/0891-5849(88)90101-3}, abstractNote={The antioxidant enzymes, catalase and superoxide dismutase, are inactivated upon exposure to ozone. In this study, the mechanism of this inactivation was examined using catalase as a model system. The data show that the inactivation of catalase is dependent on ozone concentration, time of exposure, and pH. Loss of catalase activity is accompanied with loss of the heme spectra. Tiron, desferal-Mn, trolox-c, and pyruvate protect the enzyme against ozone inactivation. SOD is less effective due to its inactivation by ozone. On the other hand, alcohols do not provide significant protection. The data suggest the possible involvement of superoxide radicals in the inactivation of catalase by ozone.}, number={5-6}, journal={Free Radical Biology and Medicine}, publisher={Elsevier BV}, author={Whiteside, Catherine and Hassan, Hosni M.}, year={1988}, month={Jan}, pages={305–312} }
 @article{lee_hassan_1988, title={Stability and expression of a plasmid-containing killer toxin cDNA in batch and chemostat cultures ofsaccharomyces cerevisiae}, volume={31}, ISSN={0006-3592 1097-0290}, url={http://dx.doi.org/10.1002/bit.260310804}, DOI={10.1002/bit.260310804}, abstractNote={A chimeric plasmid (pYT760-ADH1) containing the yeast killer toxin-immunity cDNA was transformed into a leucine-histidine mutant (AH22) and into four industrial toxin-sensitive yeasts. The chimeric plasmid was very stable and expressed toxin production (89.5 +/- 4.8% killer cells) in two of the transformed yeasts that contained the 2mu plasmid, but was lost within 10 generations from two other transformed pickle yeasts that did not contain the 2mu plasmid. It suggested that plasmid stability was dependent on the presence of the 2mu plasmid which is naturally present in some yeasts. The plasmid was extremely stable (100% killer cells) and expressed more toxin in the mutant strain AH22. The effects of dilution rate, D(h(-1)) on plasmid stability and toxin expression were studied in transformed AH22 (AH22/T3) and Montrachet 522 (522/T1) wine yeast grown in glucose-limited chemostat cultures. The results show that killer toxin production by AH22/T3 cells increased as a function of D(h(-1)) and that plasmid stability reached 100% at D >/= 0.09 +/- 0.01 h(-1). However, with Montrachet 522/T1 transformed cells, 100% plasmid stability was seen at D >/= 0.18 +/- 0.02. h(-1). We also challenged the AH22/T3 in chemostat culture (D = 0.25 h(-1)) with an equal number of untransformed cells (AH22). Transformed cells dominated the population (100%) within 8-10 h of growth, a time equivalent to two mean residence time.}, number={8}, journal={Biotechnology and Bioengineering}, publisher={Wiley}, author={Lee, Fang-Jen S. and Hassan, H. M.}, year={1988}, month={May}, pages={783–789} }
 @inproceedings{hassan_schellhorn_1988, title={Superoxide dismutase: an antioxidant defense enzyme}, volume={82}, booktitle={UCLA Symposia on Molecular and Cellular Biology}, author={Hassan, H.M. and Schellhorn, H.E.}, year={1988}, pages={183–193} }
 @article{schiavone_hassan_1988, title={The role of redox in the regulation of manganese-containing superoxide dismutase biosynthesis in Escherichia coli.}, volume={263}, ISSN={0021-9258}, url={http://dx.doi.org/10.1016/s0021-9258(18)68920-3}, DOI={10.1016/s0021-9258(18)68920-3}, abstractNote={The manganese-containing superoxide dismutase in Escherichia coli is an inducible enzyme that protects cells against oxygen toxicity. The manganese-enzyme is induced by oxygen, nitrate, redox active compounds that react with oxygen to generate superoxide radicals, as well as iron chelators. In order to test the hypothesis that the redox state of the cell is involved in regulating manganese-superoxide dismutase biosynthesis, we studied the effects of several oxidants on growth and superoxide dismutase biosynthesis. The data showed, that under anaerobic conditions, the active manganese-enzyme is induced in the presence of potassium ferricyanide, copper-cyanide complex, ammonium persulfate, and hydrogen peroxide. Western blot analysis revealed that the induction of manganese-superoxide dismutase by the oxidants is associated with de novo protein biosynthesis. Potassium ferricyanide and hydrogen peroxide induced the enzyme under aerobic conditions as well. It is concluded that the redox state of the cell possibly influences the biosynthesis and/or activity of an iron-containing repressor protein that serves to negatively regulate manganese-superoxide dismutase biosynthesis.}, number={9}, journal={Journal of Biological Chemistry}, publisher={Elsevier BV}, author={Schiavone, J R and Hassan, H M}, year={1988}, month={Mar}, pages={4269–4273} }
 @article{schellhorn_hassan_1988, title={Transcriptional regulation of katE in Escherichia coli K-12}, volume={170}, ISSN={0021-9193 1098-5530}, url={http://dx.doi.org/10.1128/jb.170.9.4286-4292.1988}, DOI={10.1128/jb.170.9.4286-4292.1988}, abstractNote={Escherichia coli produces two distinct species of catalase, hydroperoxidases I and II, which differ in kinetic properties and regulation. To further examine catalase regulation, a lacZ fusion was placed into one of the genes that is involved in catalase synthesis. Transductional mapping revealed the fusion to be either allelic with or very close to katE, a locus which together with katF controls the synthesis of the aerobically inducible hydroperoxidase (hydroperoxidase II). katE was expressed under anaerobic conditions at levels that were approximately one-fourth of those found in aerobically grown cells and was found to be induced to higher levels in early-stationary-phase cells relative to levels of exponentially growing cells under both anaerobic and aerobic conditions. katE was fully expressed in air and was not further induced when the growth medium was sparged with 100% oxygen. Expression of katE was unaffected by the addition of hydrogen peroxide or by the presence of additional lesions in oxyR or sodA, indicating that it is not part of the oxyR regulon. When katF::Tn10 was introduced into a katE::lacZ strain, beta-galactosidase synthesis was largely eliminated and was no longer inducible, suggesting that katF is a positive regulator of katE expression.}, number={9}, journal={Journal of Bacteriology}, publisher={American Society for Microbiology}, author={Schellhorn, H E and Hassan, H M}, year={1988}, month={Sep}, pages={4286–4292} }
 @article{lee_hassan_1987, title={Biosynthesis of superoxide dismutase and catalase in chemostat culture of Saccharomyces cerevisiae}, volume={26}, ISSN={0175-7598 1432-0614}, url={http://dx.doi.org/10.1007/bf00253027}, DOI={10.1007/bf00253027}, number={6}, journal={Applied Microbiology and Biotechnology}, publisher={Springer Science and Business Media LLC}, author={Lee, Fang-Jen S. and Hassan, Hosni M.}, year={1987}, month={Sep}, pages={531–536} }
 @article{schiavone_hassan_1987, title={Biosynthesis of superoxide dismutase in eight prokaryotes: Effects of oxygen, paraquat and an iron chelator}, volume={42}, ISSN={0378-1097 1574-6968}, url={http://dx.doi.org/10.1111/j.1574-6968.1987.tb02295.x}, DOI={10.1111/j.1574-6968.1987.tb02295.x}, abstractNote={The effect of oxygen, paraquat (PQ2+; 1,1′-dimethyl-4,4′-bipyridinium dichloride) and 2,2′-dipyridyl (2,2′-DP) on the synthesis of superoxide dismutase (SOD) in various microorganisms was examined to determine whether the control of SOD biosynthesis in other prokaryotes is similar to that in Escherichia coli. All of the strains tested, with the exception of Alcaligenes faecalis, exhibited SOD levels proportional to the concentration of oxygen in the growth media. Paraquat induced SOD in all of the strains surveyed except Staphylococcus epidermidis, Streptococcus faecalis, and Listeria monocytogenes. The iron chelator, 2,2′-DP, induced SOD in Proteus vulgaris, Enterobacter cloacae and Staphylococcus aureus, but decreased the activity of SOD in A. faecalis and Pseudomonas aeruginosa and had no effect in S. epidermidis, S. faecalis or L. monocytogenes. The data indicate that the induction of SOD in P. vulgaris, E. cloacae, and Salmonella typhimurium is similar to that found in E. coli and suggest that the mechanism of SOD regulation in E. coli may be representative of the Enterobacteriaceae family as a whole.}, number={1}, journal={FEMS Microbiology Letters}, publisher={Oxford University Press (OUP)}, author={Schiavone, Joan R. and Hassan, Hosni M.}, year={1987}, month={Jun}, pages={33–38} }
 @article{lee_hassan_1987, title={Effect of oxygen tension on stability and expression of a killer toxin chimeric plasmid in a chemostat culture of Saccharomyces cerevisiae}, volume={27}, ISSN={0175-7598 1432-0614}, url={http://dx.doi.org/10.1007/bf00257256}, DOI={10.1007/bf00257256}, number={1}, journal={Applied Microbiology and Biotechnology}, publisher={Springer Science and Business Media LLC}, author={Lee, Fang-JenS. and Hassan, H.M.}, year={1987}, month={Oct}, pages={72–74} }
 @misc{hassan_1987, title={Free Radicals in Health and Disease}, author={Hassan, H}, year={1987}, month={Sep} }
 @article{whiteside_hassan_1987, title={Induction and inactivation of catalase and superoxide dismutase of Escherichia coli by ozone}, volume={257}, ISSN={0003-9861}, url={http://dx.doi.org/10.1016/0003-9861(87)90591-1}, DOI={10.1016/0003-9861(87)90591-1}, abstractNote={Oxyradicals have been implicated in ozone (O3) toxicity and in other oxidant stress. In this study, we investigated the effects of O3 on the biosynthesis of the antioxidant enzymes catalase and superoxide dismutase in Escherichia coli to determine their role in the defense against ozone toxicity. Inhibition of growth and loss of viability were observed in cultures exposed to ozone. Results also showed an increase in the activities of catalase and superoxide dismutase in cultures exposed to ozone, which was shown to be due to true induction rather than activation of preexisting apoproteins. Cessation of O3 exposure resulted in 30 min of continual high rate of catalase biosynthesis followed by a gradual decrease in the level of the enzyme approaching that of control cultures. This decrease was attributed to a concomitant cessation of de novo enzyme synthesis and dilution of preexisting enzyme by cellular growth. Ozonation of cell-free extracts showed that superoxide dismutase and catalase are subject to oxidative inactivation by ozone. In vivo induction of these enzymes may represent an adaptive response evolved to protect cells against ozone toxicity.}, number={2}, journal={Archives of Biochemistry and Biophysics}, publisher={Elsevier BV}, author={Whiteside, Catherine and Hassan, Hosni M.}, year={1987}, month={Sep}, pages={464–471} }
 @article{hassan_moody_1987, title={Regulation of manganese-containing superoxide dismutase in Escherichia coli. Anaerobic induction by nitrate.}, volume={262}, ISSN={0021-9258}, url={http://dx.doi.org/10.1016/s0021-9258(18)45506-8}, DOI={10.1016/s0021-9258(18)45506-8}, abstractNote={We have previously demonstrated that iron plays an important regulatory role in the biosynthesis of manganese-containing superoxide dismutase in Escherichia coli (Moody, C.S., and Hassan, H.M. (1984) J. Biol. Chem. 259, 12821-12825). In this study, we demonstrated that the effect of iron is at the transcriptional/translational level, whereas the effect of manganese is at the post-translational level. The anaerobic additions of nitrate or nitrate plus paraquat caused a positive change in the redox potential of the growth medium and concomitant induction of the manganese-superoxide dismutase in the cells. By using 59Fe, we were able to identify two unique proteins that were constitutively made, but contained iron only under conditions where the synthesis of manganese-superoxide dismutase was fully repressed. The presence of a multicopy plasmid carrying the manganese-superoxide dismutase gene resulted in the anaerobic expression of the gene presumably by neutralizing the limited number of repressor molecules found in the cells. In toto, the data support our previously proposed model for a negatively controlled operon where the repressor molecule is envisioned as an allosteric redox sensing protein. Conditions known to oxidize or to deplete the iron are also found to cause induction of the manganese-superoxide dismutase albeit the absence of dioxygen.}, number={35}, journal={Journal of Biological Chemistry}, publisher={Elsevier BV}, author={Hassan, H M and Moody, C S}, year={1987}, month={Dec}, pages={17173–17177} }
 @inbook{hassan_kao_1986, title={An alternate defense mechanism against paraquat toxicity in Escherichia coli}, booktitle={Superoxide and Superoxide Dismutase in Chemistry, Biology and Medicine}, publisher={Elsevier Science}, author={Hassan, H.M. and Kao, S.}, editor={Rotilio, G.Editor}, year={1986}, pages={354–357} }
 @article{lee_hassan_1986, title={Biosynthesis of superoxide dismutase and catalase inSaccharomyces cerevisiae: effects of oxygen and cytochromec deficiency}, volume={1}, ISSN={0169-4146 1476-5535}, url={http://dx.doi.org/10.1007/bf01569271}, DOI={10.1007/bf01569271}, abstractNote={Two strains ofSaccharomyces cerevisiae were used to study the synthesis of superoxide dismutase. One strain (cytochromec-deficient) contained 5–10% of the normal amounts of total cytochromec, while the other strain was a wild type. The cytochromec-deficient mutant had lower specific growth rate, growth yield, and oxygen uptake than the wild type. The superoxide dismutase and catalase activities, in both strains, were significantly lower under anaerobic than under aerobic conditions. Furthermore, under aerobic conditions the mutant contained higher levels of superoxide dismutase than the wild type which may be attributed to the higher intracellular flux of superoxide radicals caused by the cytochromec deficiency. The mutant also showed a lower level of catalase which was due to glucose repression.}, number={3}, journal={Journal of Industrial Microbiology}, publisher={Oxford University Press (OUP)}, author={Lee, Fang-Jen and Hassan, Hosni M.}, year={1986}, month={Jul}, pages={187–193} }
 @article{himelbloom_hassan_1986, title={Effects of cysteine on growth, protease production, and catalase activity of Pseudomonas fluorescens}, volume={51}, ISSN={0099-2240 1098-5336}, url={http://dx.doi.org/10.1128/aem.51.2.418-421.1986}, DOI={10.1128/aem.51.2.418-421.1986}, abstractNote={Cysteine inhibits growth of and protease production by Pseudomonas fluorescens NC3. Catalase activity in P. fluorescens NC3 was increased by cysteine. The addition of exogenous hydrogen peroxide did not increase catalase activity, thus suggesting a role for the endogenous generation of hydrogen peroxide via the autoxidation of cysteine.}, number={2}, journal={Applied and Environmental Microbiology}, publisher={American Society for Microbiology}, author={Himelbloom, B H and Hassan, H M}, year={1986}, month={Feb}, pages={418–421} }
 @inbook{hassan_lee_1986, title={Effects of cytochrome c deficiency, paraquat and copper on the biosynthesis of copper zinc superoxide dismutase and catalase in Saccharomyces cerevisiae}, booktitle={Superoxide and Superoxide Dismutase in Chemistry, Biology and Medicine}, publisher={Elsevier Science}, author={Hassan, H.M. and Lee, F.J.}, editor={Rotilio, G.Editor}, year={1986}, pages={300–303} }
 @inbook{hassan_moody_1986, title={Regulation of the synthesis of superoxide dismutase in procaryotes}, booktitle={Superoxide and Superoxide Dismutase in Chemistry, Biology and Medicine}, publisher={Elsevier Science}, author={Hassan, H.M. and Moody, C.S.}, editor={Rotilo, G.Editor}, year={1986}, pages={274–279} }
 @inproceedings{hassan_1986, title={Role of Superoxide Dismutase in Cellular Protection}, author={Hassan, H.}, year={1986} }
 @article{kao_hassan_1985, title={Biochemical characterization of a paraquat-tolerant mutant of Escherichia coli.}, volume={260}, ISSN={0021-9258}, url={http://dx.doi.org/10.1016/s0021-9258(19)85108-6}, DOI={10.1016/s0021-9258(19)85108-6}, abstractNote={The biochemical basis for paraquat tolerance was investigated using one of the paraquat-resistant Escherichia coli mutants previously isolated. When grown in the absence of paraquat (PQ2+), the specific activities of glucose-6-phosphate dehydrogenase and NADPH:PQ2+-diaphorase, both required for the expression of PQ2+ toxicity, were comparable in the wild type and the mutant. However, growth in the presence of 1 mM PQ2+ resulted in greater induction of these two enzymes in the wild type than in the mutant. Nevertheless, when the mutant was grown in 50 mM PQ2+, the activities of these two enzymes were comparable to those of the wild type grown in the presence of 1 mM PQ2+. Measurement of cyanide-resistant respiration, an indication of intracellular superoxide generation, showed that the intracellular flux of superoxide mediated by subsaturating concentrations of paraquat was significantly lower in the mutant than in the wild type. Extracellular superoxide formation, as measured by superoxide dismutase-inhibitable cytochrome c reduction, was higher in the wild type than in the mutant whether grown in the absence or the presence of PQ2+. The mutant did not show cross-resistance toward juglone or plumbagin, compounds known to exacerbate superoxide generation. The kinetics of [14C]PQ2+ uptake showed that the wild type accumulated PQ2+ against a concentration gradient, whereas the mutant seemed to do so only by facilitated diffusion. The results indicate that the impaired paraquat uptake system in the mutant results in the physiological and biochemical differences observed between the wild type and mutant.}, number={19}, journal={Journal of Biological Chemistry}, publisher={Elsevier BV}, author={Kao, S M and Hassan, H M}, year={1985}, month={Sep}, pages={10478–10481} }
 @article{lee_hassan_1985, title={Biosynthesis of superoxide dismutase in Sacchromyces cerevisiae: Effects of paraquat and copper}, volume={1}, ISSN={0748-5514}, url={http://dx.doi.org/10.1016/0748-5514(85)90138-2}, DOI={10.1016/0748-5514(85)90138-2}, abstractNote={Growth of Saccharomyces cerevisiae in the presence of paraquat caused an increase the intracellular flux of superoxide radicals and in superoxide dismutase biosynthesis. The addition of copper to the growth medium also elicited an increase in superoxide dismutase levels. A cytochrome c deficient mutant strain was found to be more responsive than the wild type strain to paraquat and/or copper by increasing its copper-zinc superoxide dismutase. Catalase activity in both strains was not significantly affected by paraquat and/or copper.}, number={4}, journal={Journal of Free Radicals in Biology & Medicine}, publisher={Elsevier BV}, author={Lee, Fang-Jen and Hassan, Hosni M.}, year={1985}, month={Jan}, pages={319–325} }
 @article{kao_hassan_1985, title={Isolation of paraquat-resistant mutants ofEscherichia coli: lack of correlation between resistance and the activity of superoxide dismutase}, volume={28}, ISSN={0378-1097 1574-6968}, url={http://dx.doi.org/10.1111/j.1574-6968.1985.tb00771.x}, DOI={10.1111/j.1574-6968.1985.tb00771.x}, abstractNote={Paraquat-resistant Escherichia coli mutants were isolated. The mutants were 10- to 50-fold more resistant to paraquat than the wild type. The wild type was more responsive to the presence of paraquat by inducing higher levels of the manganese-containing superoxide dismutase (MnSOD). Thus, in minimal medium, 0.1 mM paraquat caused a 5-fold increase in MnSOD in the wild type while it had no effect on the level of MnSOD in the mutants. Yet, 50 mM paraquat exerted a dramatic induction of SOD in the mutant strains when grown in trypticase soy yeast extract (TSY) medium. In TSY medium, catalase was not significantly affected by paraquat in all the strains tested. Resistance to paraquat in these mutant strains is, therefore, unrelated to their capacity to detoxify superoxide or hydrogen peroxide.}, number={1}, journal={FEMS Microbiology Letters}, publisher={Oxford University Press (OUP)}, author={Kao, Su Mei and Hassan, Hosni M.}, year={1985}, month={Jun}, pages={93–97} }
 @inbook{hassan_1985, place={Florida, US}, title={Manipulation of Superoxide Dismutase Levels in Procaryotes}, booktitle={CRC Handbook of Methods for Oxygen Radical Research}, publisher={CRC Press Inc.}, author={Hassan, H.M.}, editor={Greenwald, R.Editor}, year={1985}, pages={353–358} }
 @article{himelbloom_hassan_1985, title={Optimization of the hide powder azure assay for quantitating the protease of Pseudomonas fluorescens}, volume={4}, ISSN={0167-7012}, url={http://dx.doi.org/10.1016/0167-7012(85)90021-1}, DOI={10.1016/0167-7012(85)90021-1}, abstractNote={Abstract The extracellular protease of Pseudomonas fluorescens NC 3 was optimally active at 40°C in a reaction mixture containing: 50 mM HEPES ( N -2-hydroxyethylpiperazine- N ′-2-ethanesulfonic acid) buffer (pH 6.6), 0.5 mM CaCl 2 , and 25 mg hide powder azure in 5 ml total volume. Divalent cation chelators, i.e., EDTA, o -phenanthroline, citrate or phosphate, inhibited the enzyme. Protease production by P. fluorescens NC 3 was initiated during late-logarithmic-growth phase in a sodium caseinate medium and reached its maximum at the onset of the stationary phase.}, number={2}, journal={Journal of Microbiological Methods}, publisher={Elsevier BV}, author={Himelbloom, Brian H. and Hassan, Hosni M.}, year={1985}, month={Aug}, pages={59–66} }
 @article{hancock_hassan_1985, title={Regulation of the manganese-containing superoxide dismutase is independent of the inducible DNA repair system in Escherichia coli.}, volume={260}, ISSN={0021-9258}, url={http://dx.doi.org/10.1016/s0021-9258(17)38818-x}, DOI={10.1016/s0021-9258(17)38818-x}, abstractNote={Studies on the induction of the manganese-containing superoxide dismutase in several strains of Escherichia coli with different mutations in recA and lexA revealed that the inductions of the Mn-isozyme and of the SOS system by oxygen free radicals are not coregulated. We also studied the synthesis of the manganese-superoxide dismutase in the temperature-dependent, protease-constitutive strain recA441(tif-1) that also contained a lac fusion in an SOS gene. A shift to the temperature at which recA441 has constitutive protease activity did not induce Mn-superoxide dismutase but did induce beta-galactosidase. The data clearly demonstrate that induction of the Mn-superoxide dismutase is independent of the SOS system.}, number={24}, journal={Journal of Biological Chemistry}, publisher={Elsevier BV}, author={Hancock, L C and Hassan, H M}, year={1985}, month={Oct}, pages={12954–12956} }
 @article{moody_hassan_1984, title={Anaerobic biosynthesis of the manganese containing superoxide dismutase in Escherichia coli}, volume={259}, DOI={10.1016/S0021-9258(18)90820-3}, abstractNote={Iron, particularly in the ferrous state plays a role in regulating the biosynthesis of the manganese superoxide dismutase (MnSOD) in Escherichia coli B. Addition of iron has a repressive effect on the synthesis of MnSOD under normal or inducing conditions (i.e. in the presence of paraquat). Addition of manganese to cultures already depressed for MnSOD biosynthesis causes a further increase in the amount of active enzyme, however, this effect is also abolished by the addition of iron. Removal of metals from the growth medium by Chelex 100 also derepresses the synthesis of MnSOD but repletion of the medium with iron abolishes this effect. Chelators specific for Fe2+, 2,2'-dipyridyl, and 1,10-phenanthroline, cause a 5-7-fold increase in MnSOD. Removal of iron also increases the synthesis of MnSOD in the absence of oxygen. A model is presented to account for the observed effects of oxygen, superoxide anion, and chelators on the increased synthesis of MnSOD. In this model, the regulatory repressor for MnSOD biosynthesis is envisioned as being an iron-containing protein.}, number={20}, journal={Journal of Biological Chemistry}, author={Moody, C.S. and Hassan, H.M.}, year={1984}, month={Oct}, pages={12821–12825} }
 @inbook{hassan_1984, title={Chemistry and Biochemistry of Oxygen and of Its Partially Reduced Derivatives}, booktitle={Oxygen: An In Depth Study of Its Pathophysiology}, publisher={Undersea Medical Society, Inc}, author={Hassan, H.M.}, editor={Totter, J.R. and Gottlieb, S.F. and Longmuir, I.S.Editors}, year={1984}, pages={307–340} }
 @article{hassan_moody_1984, title={Induction of the manganese-containing superoxide dismutase inEscherichia coliby nalidixic acid and by iron chelators}, volume={25}, ISSN={0378-1097 1574-6968}, url={http://dx.doi.org/10.1111/j.1574-6968.1984.tb01463.x}, DOI={10.1111/j.1574-6968.1984.tb01463.x}, abstractNote={Nalidixic acid caused a significant increase in the Mn-containing superoxide dismutase (MnSOD) of Escherichia coli. The maximum stimulatory effect of nalidixic acid on MnSOD biosynthesis was observed at 0.1 mM. The stimulatory effect of nalidixic acid was not due to increases in the intracellular flux of O−2, but rather to its ability to chelate Fe2+. Furthermore, 2,2′-dipyridyl and 1,10-phenanthroline were shown to cause a 7- to 20-fold increase in the MnSOD of E. coli. It is proposed that the repressor for MnSOD is an iron-containing protein.}, number={2-3}, journal={FEMS Microbiology Letters}, publisher={Oxford University Press (OUP)}, author={Hassan, Hosni M. and Moody, Carmella S.}, year={1984}, month={Dec}, pages={233–236} }
 @inbook{hassan_fridovich_1984, place={North Holland}, title={Oxygen toxicity in prokaryotes}, booktitle={The Biology and Chemistry of Active Oxygen}, publisher={Elsevier}, author={Hassan, H.M. and Fridovich, I.}, editor={Bannister, J.V.Editor}, year={1984}, pages={128–138} }
 @inbook{hassan_1984, place={NY}, title={Superoxide Dismutase: An Antioxidant Defense Enzyme. In Free Radicals in Molecular Biology, Aging and Disease}, ISBN={0881670480 9780881670486}, booktitle={Free Radicals in Molecular Biology, Aging and Disease}, publisher={Raven Press}, author={Hassan, H.M.}, editor={Armstrong, D. and Sohal, R.S. and Cutler, R.G. and Slater, T.F.Editors}, year={1984}, pages={77–85} }
 @article{hassan_bhatti_white_1984, title={Superoxide dismutase, catalase and peroxidase in four strains of Neisseria meningitidis of different virulence}, volume={25}, ISSN={0378-1097 1574-6968}, url={http://dx.doi.org/10.1111/j.1574-6968.1984.tb01378.x}, DOI={10.1111/j.1574-6968.1984.tb01378.x}, abstractNote={The effects of growth media on superoxide dismutase (SOD), catalase and peroxidase were compared in cell-free extracts from four strains of Neisseria meningitidis. The highly virulent strains, DRES-14 and M-1011, were consistently higher in SOD and catalase than the less virulent strains, DRES-03 and DRES-04. Cells grown in brain-heart infusion medium contained the highest levels of catalase. N. meningitidis contained one electrophoretic SOD band which was identified as iron-containing SOD (FeSOD). It was also shown that the presence of catalase could yield an artifactual SOD-band when the SOD activity stain is performed in the presence of 10 mM H2O2, normally required to inactivate and identify FeSODs.}, number={1}, journal={FEMS Microbiology Letters}, publisher={Oxford University Press (OUP)}, author={Hassan, H.M. and Bhatti, A.R. and White, L.A.}, year={1984}, month={Nov}, pages={71–74} }
 @inbook{hassan_moody_1984, place={San Diego, CA}, series={Methods in Enzymology}, title={[30] Determination of the mutagenicity of oxygen free radicals using microbial systems}, ISBN={9780121820053}, ISSN={0076-6879}, url={http://dx.doi.org/10.1016/s0076-6879(84)05033-3}, DOI={10.1016/s0076-6879(84)05033-3}, abstractNote={Publisher Summary Increased oxygen tension has been known, for more than two decades, to cause chromosomal breaks and mutations both in eukaryotes and in prokaryotes. Recently, it has been shown that the physiological concentrations of oxygen (-5% O 2 ) are mutagenic in certain oxygen-sensitive histidine auxotrophs of Salmonella typhimurium strain TA100. A basic understanding of these deleterious effects of oxygen came with the advent of the theory of oxygen toxicity. This theory states that the partially reduced intermediates of oxygen––the superoxide anion (O 2 - ), hydrogen peroxide (H 2 O 2 ), and the hydroxyl radical (OH·)––are the damaging agents. In accordance with this theory, it has been shown that ionizing radiation generates oxygen free radicals, that superoxide radicals can indirectly cause DNA strand scission in vitro , and that oxygen free radicals generated by paraquat (PQ) are mutagenic. This chapter presents methods for assessing the mutagenicity of oxygen free radicals in microbial systems. These methods are usually rapid, simple, and inexpensive.}, booktitle={Oxygen Radicals in Biological Systems}, publisher={Academic Press/Elsevier}, author={Hassan, Hosni M. and Moody, Carmella S.}, editor={Packer, LesterEditor}, year={1984}, pages={254–263}, collection={Methods in Enzymology} }
 @inbook{hassan_1984, place={San Diego, CA}, series={Methods in Enzymology}, title={[53] Determination of microbial damage caused by oxygen free radicals, and the protective role of superoxide dismutase}, ISBN={9780121820053}, ISSN={0076-6879}, url={http://dx.doi.org/10.1016/s0076-6879(84)05056-4}, DOI={10.1016/s0076-6879(84)05056-4}, abstractNote={Publisher Summary The importance of superoxide dismutase (SOD) as a defense against the cellular damage caused by oxygen free radicals has been extensively demonstrated in microbial systems. Most of the studies have been carried out with gram-negative enteric organisms, but a few studies have been done using gram-positive staphylococci. In this type of study, a generator of oxygen free radicals and a test organism are required. Cellular damage may be assessed by the enumeration of viable cells, loss of some vital cellular function, such as transport of nutrients, structural changes as observed by electron microscopy or by the release of some intracellular marker enzymes. This chapter presents methods for generating oxygen free radicals, for manipulating the cellular concentration of SOD, and for assessing the damage caused by oxygen free radicals. Loss of viability is normally caused by irreparable damage to one or more of the vital cellular components. Therefore, the use of specific repair deficient mutants may further amplify the damage and loss of viability.}, booktitle={Oxygen Radicals in Biological Systems}, publisher={Academic Press/Elsevier}, author={Hassan, Hosni M.}, editor={Packer, LesterEditor}, year={1984}, pages={404–412}, collection={Methods in Enzymology} }
 @inbook{hassan_1984, place={San Diego, CA}, series={Methods in Enzymology}, title={[69] Exacerbation of superoxide radical formation by Paraquat}, ISBN={9780121820053}, ISSN={0076-6879}, url={http://dx.doi.org/10.1016/s0076-6879(84)05072-2}, DOI={10.1016/s0076-6879(84)05072-2}, abstractNote={Paraquat, also known as methyl viologen, is the active ingredient of many commercially available broad-spectrum herbicides. Paraquat seems to be universally toxic both in prokaryotes and eukaryotes, and incidents of fatal paraquat poisonings have been reported in man and animals. Crude cell-free extracts from plants, animals, and bacterial origins have been shown to reduce PQ2+ to PQ·+in the presence of nicotinamide adenine dinucleotide phosphate (NADPH) or an NADPH-generating system (i.e., glucose-6-phosphate, glucose-6-phosphate dehydrogenase, and NADP+). The enzyme that reduces PQ2+ is a diaphorase-like enzyme usually present in the cytoplasm and specific for NADPH. Paraquat is readily reduced by a single electron to a stable but dioxygen-sensitive monocation radical (PQ·+). The reaction between the paraquat radical and dioxygen (O2) generates the true toxic species, the superoxide radical (O2-), and subsequently hydrogen peroxide (H2O2). Hydroxyl radicals (OH·) may also be generated because of secondary interactions between O2- and H2O2. This chapter presents methods for measuring and identifying the partially reduced oxygen species generated during the reaction of PQ·+ and O2.}, booktitle={Oxygen Radicals in Biological Systems}, publisher={Academic Press/Elsevier}, author={Hassan, Hosni M.}, editor={Packer, LesterEditor}, year={1984}, pages={523–532}, collection={Methods in Enzymology} }
 @misc{hassan_1983, title={Antioxidant Enzymes and Aging}, author={Hassan, H.}, year={1983}, month={Oct} }
 @misc{hassan_1983, title={Oxygen}, author={Hassan, H.}, year={1983}, month={Jun} }
 @inbook{hassan_1983, place={Holland}, title={Oxygen toxicity and mutagenicity in procaryotes}, volume={1}, booktitle={Oxy Radicals and Their scavengers Systems: Molecular Aspects}, publisher={Elsevier}, author={Hassan, H.M.}, editor={Cohen, G. and Greenwald, R.Editors}, year={1983}, pages={198–206} }
 @article{von stein_barber_hassan_1982, title={Biosynthesis of oxygen-detoxifying enzymes in Bdellovibrio stolpii}, volume={152}, ISSN={0021-9193 1098-5530}, url={http://dx.doi.org/10.1128/jb.152.2.792-796.1982}, DOI={10.1128/jb.152.2.792-796.1982}, abstractNote={Axenically grown Bdellovibrio stolpii (i.e., grown independently of the host) was examined for superoxide dismutase, catalase, and peroxidase activities. Kinetics of enzyme synthesis were determined for aerobically grown cultures and for cultures exposed to 100% oxygen. Enzymatic activities varied with the age of the culture. Normally grown cultures exhibited maximum activity during the first 10 h of growth and again as the stationary phase was approached, beginning at about 48 h. Polyacrylamide gel electropherograms of cell-free extracts revealed that B. stolpii contained one major band (1) and two minor bands (II, III) of superoxide dismutase activity. Each of these enzymes was inactivated by H2O2, indicating that they were iron-containing enzymes. Manganese-containing superoxide dismutase was not detected in B. stolpii. Increased oxygenation did not appreciably stimulate enzyme synthesis, for only superoxide dismutase was induced, reaching maximum activity at 10 h and then rapidly falling to normal levels. Superoxide dismutase appears to be the main enzymatic defense against oxygen toxicity in B. stolpii. Induction of superoxide dismutase with 100% oxygen was manifested as an increase in the intensities of the two minor bands of activity, suggesting that isozyme I is constitutive, whereas isozymes II and III are inducible. The induction of isozymes II and III by 100% oxygen was prevented by an inhibitor of protein biosynthesis, chloramphenicol.}, number={2}, journal={Journal of Bacteriology}, publisher={American Society for Microbiology}, author={Von Stein, R S and Barber, L E and Hassan, H M}, year={1982}, month={Nov}, pages={792–796} }
 @inbook{hassan_fridovich_1982, place={Oxford, UK}, title={Exacerbations of Oxygen Toxicity by Redox Active Compounds}, ISBN={9780080244211}, url={http://dx.doi.org/10.1016/b978-0-08-024421-1.50011-2}, DOI={10.1016/b978-0-08-024421-1.50011-2}, booktitle={Oxidases and Related Redox Systems}, publisher={Pergamon/Elsevier}, author={Hassan, H. Moustafa and Fridovich, Irwin}, editor={King, Tsso E. and Mason, Howard S. and Morrison, MartinEditors}, year={1982}, pages={151–167} }
 @article{moody_hassan_1982, title={MUTAGENICITY OF OXYGEN FREE-RADICALS}, volume={79}, ISSN={["0027-8424"]}, DOI={10.1073/pnas.79.9.2855}, abstractNote={Paraquat (1,1'-dimethyl-4,4'-bipyridinium dichloride) was used as an intracellular generator of oxygen free radicals and was found to be highly mutagenic for Salmonella typhimurium. It caused both base-pair substitution and frameshift mutations. Paraquat was much more toxic and mutagenic in a simple nutritionally restricted medium than in a rich complex medium. The mutagenicity of paraquat was dependent upon the presence of a supply of both electrons and oxygen. Cells containing high levels of superoxide dismutase (superoxide:superoxide oxidoreductase, EC 1.15.1.1) were more resistant to the toxicity and the mutagenicity of paraquat than were cells containing normal levels of this enzyme. The mutagenicity of paraquat thus appears to be due to its ability to exacerbate the intracellular production of superoxide radicals.}, number={9}, journal={PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA-BIOLOGICAL SCIENCES}, author={MOODY, CS and HASSAN, HM}, year={1982}, pages={2855–2859} }
 @article{hassan_moody_1982, title={Superoxide dismutase protects against paraquat-mediated dioxygen toxicity and mutagenicity: studies in Salmonella typhimurium}, volume={60}, ISSN={0008-4212 1205-7541}, url={http://dx.doi.org/10.1139/y82-204}, DOI={10.1139/y82-204}, abstractNote={Paraquat is univalently reduced to the relatively stable, but oxygen-sensitive, paraquat radical (PQ.+). This PQ.+ can react with dioxygen to generate the superoxide radical, which can further generate other more deleterious species of oxygen free radicals (i.e., hydroxyl radical, OH.). These oxygen free radicals are known to cause chromosomal breaks; therefore, it was logical to postulate that paraquat is a mutagen. This proved to be the case when tested in a modified Ames test using a liquid incubation assay. Salmonella typhimurium strains TA98 and TA100 were grown in the presence of various concentrations of PQ, as well as in the presence of known mutagenic compounds: mitomycin C, azide, and proflavine. Paraquat was much more toxic and mutagenic in a simple nutritionally restricted medium than in a rich complex medium and these toxic and mutagenic effects were oxygen dependent. Furthermore, cells containing high levels of superoxide dismutase were more resistant to the toxic and mutagenic effects of paraquat than were cells containing a normal level of this enzyme.}, number={11}, journal={Canadian Journal of Physiology and Pharmacology}, publisher={Canadian Science Publishing}, author={Hassan, Hosni M. and Moody, Carmella S.}, year={1982}, month={Nov}, pages={1367–1373} }
 @article{hassan_fridovich_1981, title={Chemistry and biochemistry of superoxide dismutases}, volume={4}, journal={European Journal of Rheumatology and Inflammation}, author={Hassan, H.M. and Fridovich, I.}, year={1981}, pages={160–172} }
 @inbook{hassan_1981, place={Boston}, title={Superoxide and superoxide dismutases in Escherichia coli: threat and defense}, ISBN={0884163091 9780884163091}, booktitle={Membranes, Molecules, Toxins, and Cells}, publisher={PSG Inc}, author={Hassan, H.M.}, editor={Bloch, K. and Bolis, L. and Tosteson, D.C. and Wright, J.Editors}, year={1981}, pages={123–133} }
 @book{hassan_hassan_1981, title={Vacuum Drum Planters}, number={US4306509A}, author={Hassan, A.E. and Hassan, H.}, year={1981}, month={Dec} }
 @inbook{hassan_fridovich_1980, place={North Holland}, title={Impermeability of the Escherichia coli cell envelope to superoxide radical}, volume={11B}, booktitle={Developments in Biochemistry: Biological and Clinical Aspects of Superoxide and Superoxide Dismutase}, publisher={Elsevier North Holland}, author={Hassan, H.M. and Fridovich, I.}, editor={Bannister, W.H. and Bannister, J.V.Editors}, year={1980}, pages={57–71} }
 @article{hassan_dougherty_fridovich_1980, title={Inhibitors of superoxide dismutases: A cautionary tale}, volume={199}, ISSN={0003-9861}, url={http://dx.doi.org/10.1016/0003-9861(80)90290-8}, DOI={10.1016/0003-9861(80)90290-8}, abstractNote={Abstract An extensive search resulted in the identification of pamoic acid as an inhibitor of superoxide dismutases. Pamoic acid appeared to rapidly and reversibly inhibit all types of superoxide dismutases and did so in both the cytochrome c reduction and in the dianisidine photooxidation assays, used to measure this activity. It could nevertheless be shown that pamoic acid did not at all inhibit superoxide dismutase but rather diminished the sensitivity of the assays. The mechanism proposed to account for this effect involved oxidation of pamoate, by O2−, to yield a pamoate radical which can then reduce cytochrome c or oxidize pyrogallol. Pamoate thus competes with superoxide dismutase for the available O2−, without affecting the observable effects of that O2− upon cytochrome c or upon pyrogallol. It consequently makes these assays less responsive to superoxide dismutase, while appearing to be without effect in the absence of superoxide dismutase. Several of the predicted consequences of this proposal were affirmed. Other workers, interested in finding inhibitors for superoxide dismutases, are hereby forwarned of this subtle snare.}, number={2}, journal={Archives of Biochemistry and Biophysics}, publisher={Elsevier BV}, author={Hassan, H.Moustafa and Dougherty, Harry and Fridovich, Irwin}, year={1980}, month={Feb}, pages={349–354} }
 @article{hassan_fridovich_1980, title={Mechanism of the antibiotic action pyocyanine}, volume={141}, ISSN={0021-9193 1098-5530}, url={http://dx.doi.org/10.1128/jb.141.1.156-163.1980}, DOI={10.1128/jb.141.1.156-163.1980}, abstractNote={Exposure of Escherichia coli growing in a rich medium to pyocyanine resulted in increased intracellular levels of superoxide dismutase and of catalase. When these adaptive enzyme syntheses were prevented by nutritional paucity, the toxic action of pyocyanine was augmented. The antibiotic action of pyocyanine was dependent upon oxygen and was diminished by superoxide dismutase and by catalase, added to the suspending medium. Pyocyanine slightly augmented the respiration of E. coli suspended in a rich medium, but greatly increased the cyanide-resistant respiration. Pyocyanine was able to cause the oxidation of reduced nicotinamide adenine dinucleotide, with O2- production, in the absence of enzymatic catalysis. It is concluded that pyocyanine diverts electron flow and thus increases the production of O2- and H2O2 and that the antibiotic action of this pigment is largely a reflection of the toxicity of these products of oxygen reduction.}, number={1}, journal={Journal of Bacteriology}, publisher={American Society for Microbiology}, author={Hassan, H M and Fridovich, I}, year={1980}, month={Jan}, pages={156–163} }
 @inbook{hassan_1980, place={Amsterdam}, series={Ciba Foundation Symposium}, title={Superoxide Dismutases}, ISBN={9780470720622 9780444901774}, ISSN={1935-4657}, url={http://dx.doi.org/10.1002/9780470720622.ch7}, DOI={10.1002/9780470720622.ch7}, abstractNote={Superoxide dismutases (EC 1.15.1.1) are metalloenzymes that catalytically scavenge the superoxide radical. They are essential for the aerobic survival of all forms of life. There are three types of superoxide dismutase, containing manganese, iron, or copper and zinc. The copper--zinc type has generally been isolated from eukaryotic cells except for the enzyme for the symbiotic marine bacterium Photobacterium leiognathi. The copper--zinc type, from different sources, has a molecular weight of about 32 000, and is composed of two identical subunits, each containing one atom of copper and one atom of zinc. The copper participates in the catalytic activity of the enzyme, while the zinc plays only a structural role. The enzyme has been resolved reversibly. Superoxide dismutases provide protection against oxygen toxicity, against compounds that cause exacerbation of oxygen toxicity, against ionizing radiation, and also against the damaging sequelae of prolonged inflammation.}, booktitle={Biological Roles of Copper}, publisher={Excerpta Medica/John Wiley & Sons, Ltd.}, author={Hassan, Hosni Moustafa}, editor={Evered, David and Lawrenson, GeralynEditors}, year={1980}, month={May}, pages={125–142}, collection={Ciba Foundation Symposium} }
 @inbook{hassan_fridovich_1980, place={San Diego, CA}, title={Superoxide Dismutases: Detoxication of a Free Radical}, ISBN={9780123800015}, url={http://dx.doi.org/10.1016/b978-0-12-380001-5.50021-9}, DOI={10.1016/b978-0-12-380001-5.50021-9}, booktitle={Enzymatic Basis of Detoxication}, publisher={Academic Press/Elsevier}, author={Hassan, H. Moustafa and Fridovich, Irwin}, editor={Jakoby, William B.`Editor}, year={1980}, pages={311–332} }
 @misc{hassan_1980, title={Superoxide and Superoxide Dismutases}, author={Hassan, H.}, year={1980}, month={Jun} }
 @misc{hassan_1979, title={Clinical Application of Superoxide Dismutase}, author={Hassan, H.}, year={1979}, month={Oct} }
 @article{hassan_fridovich_1979, title={Intracellular production of superoxide radical and of hydrogen peroxide by redox active compounds}, volume={196}, ISSN={0003-9861}, url={http://dx.doi.org/10.1016/0003-9861(79)90289-3}, DOI={10.1016/0003-9861(79)90289-3}, abstractNote={Several compounds have been found capable of diverting the electron flow in Escherichia coli and thus causing increased intracellular production of O2− and H2O2. One indication of this electron-shunting action was increased cyanide-resistant respiration and one cellular response was increased biosynthesis of the manganese-containing superoxide dismutase and of catalase. Blocking cytochrome oxidase with cyanide or azide increased the electron flow available for reduction of paraquat and presumably of the other exogenous compounds tested and thus increased their biological effects. Paraquat, pyocyanine, phenazine methosulfate, streptonigrin, juglone, menadione, plumbagin, methylene blue, and azure C were all effective in elevating intracellular production of O2− and H2O2. The effect of alloxan appeared paradoxical in that it increased cyanide-resistant respiration without significantly increasing the cell content of the manganese-superoxide dismutase and with only a small effect on the level of catalase. The alloxan effect on cyanide-resistant respiration was artifactual and was due to an oxygen-consuming reaction between alloxan and cyanide, rather than to a diversion of the intracellular electron flow. With paraquat as a representative electron-shunting compound, the increase in biosynthesis of the manganese-superoxide dismutase was prevented by inhibitors of transcription or of translation, but not by an inhibitor of replication. The increase in this enzyme activity, caused by paraquat and presumably by the other compounds, was thus due to de novo enzyme synthesis activated or derepressed at the level of transcription.}, number={2}, journal={Archives of Biochemistry and Biophysics}, publisher={Elsevier BV}, author={Hassan, H.Moustafa and Fridovich, Irwin}, year={1979}, month={Sep}, pages={385–395} }
 @inbook{hassan_krinsky_morris_pfenning_schlegel_shilo_vogels_weser_wolfe_kuenen_1979, place={NY}, title={Oxygen toxicity}, booktitle={Strategy of Microbial Life in Extreme Environments}, publisher={Dahlem Konferenzen, Verlag Chemie}, author={Hassan, H.M. and Krinsky, N.I. and Morris, J.G. and Pfenning, N. and Schlegel, H. and Shilo, M. and Vogels, G.D. and Weser, U. and Wolfe, R. and Kuenen, J.G.}, editor={Shilo, M.Editor}, year={1979}, pages={223–241} }
 @article{hassan_fridovich_1979, title={Paraquat and Escherichia coli. Mechanism of production of extracellular superoxide radical.}, volume={254}, ISSN={0021-9258}, url={http://dx.doi.org/10.1016/s0021-9258(19)86598-5}, DOI={10.1016/s0021-9258(19)86598-5}, abstractNote={Paraquat mediates a superoxide dismutase-inhibitable reduction of cytochrome c by suspensions of Escherichia coli B. Glucose was most effective in providing electrons for this cytochrome c reduction, but other nutrients could serve in this capacity, provided the cells were preconditioned by growth on these nutrients. Paraquat reduction depended upon a NADPH:paraquat diaphorase, present in the cytosol. Reduced paraquat could diffuse across the cell envelope and react with dioxygen, in the suspending medium, thus generating O2- in that compartment. Most of the paraquat reduced in the cell, under the conditions used, reoxidized in situ and most of the O2- production was thus intracellular. The partitioning of reduced paraquat between intracellular and extracellular compartments, prior to reaction with dioxygen, depended upon intracellular pO2 and any strategy which raised intracellular pO2 decreased the efflux of reduced paraquat and thus decreased extracellular O2- production. Extracellular O2- and H2O2 did contribute to cell damage in proportion to the amount produced. O2- appeared to be unable to cross the cell envelope in either direction and the only O2- which was effective in raising the rate of biosynthesis of the manganese-superoxide dismutase, was that generated within the cell.}, number={21}, journal={Journal of Biological Chemistry}, publisher={Elsevier BV}, author={Hassan, H.M. and Fridovich, I.}, year={1979}, month={Nov}, pages={10846–10852} }
 @article{fridovich_hassan_1979, title={Paraquat and the exacerbation of oxygen toxicity}, volume={4}, ISSN={0968-0004}, url={http://dx.doi.org/10.1016/0968-0004(79)90395-5}, DOI={10.1016/0968-0004(79)90395-5}, abstractNote={Abstract Paraquat subverts electron flow from the normal cytochrome pathway and increases intracellular production of superoxide radical. This radical, which is the cause of paraquat toxicity, elicits increased synthesis of the defensive enzyme, superoxide dismutase.}, number={5}, journal={Trends in Biochemical Sciences}, publisher={Elsevier BV}, author={Fridovich, Irwin and Hassan, H.Moustafa}, year={1979}, month={May}, pages={113–115} }
 @inbook{hassan_fridovich_1979, place={NY}, title={Superoxide dismutase and its role for survival in the presence of oxygen}, booktitle={Strategy of Microbial Life in Extreme Environments}, publisher={DahlemKonferenzen, Verlag Chemie [Wiley-VCH]}, author={Hassan, H.M. and Fridovich, I.}, editor={Shilo, M.Editor}, year={1979}, pages={179 193} }
 @article{hassan_fridovich_1979, title={Superoxide, Hydrogen Peroxide, and Oxygen Tolerance of Oxygen-Sensitive Mutants of Escherichia coli}, volume={1}, ISSN={1058-4838 1537-6591}, url={http://dx.doi.org/10.1093/clinids/1.2.357}, DOI={10.1093/clinids/1.2.357}, abstractNote={Oxygen-intolerant mutants of Escherichia coli K12 were selected by a replica plating technique after treatment with the mutagen, N-methyl-N′-nitro-N-nitrosoguanidine, to a lethality of 99.5%. One group of mutants had lost the ability to induce both peroxidase and catalase when exposed to oxygen but retained the ability to induce the manganese-superoxide dismutase. The second group of mutants had lost the ability to induce the activity of all these enzymes. Failure to induce peroxidase and catalase was associated with enhanced susceptibility of the bacteria to the lethal effect of oxygen. When a member of the first group of mutants was prevented from producing the manganese-superoxide dismutase by the presence of puromycin, its susceptibility to the lethal effects of oxygen was greatly increased. Two types of revertants were seen. In one group the ability to induce enzyme activity was recovered and was accompanied by the return of oxygen tolerance. Members of the other group lost the ability to respire and, therefore, no longer produced O2- and H2O2. These results indicated that enzymic scavenging of both H2O2 and O2- provides an important defense against oxygen toxicity. The parallel loss of peroxidase and catalase, which was seen in all mutants, suggests that these enzymes constitute a precursor-product pair in E. coli. The parallel loss in two of these mutants of peroxidase, catalase, and the manganese-superoxide dismutase suggests a control linkage for these enzymes, the basis of which remains to be explored.}, number={2}, journal={Clinical Infectious Diseases}, publisher={Oxford University Press (OUP)}, author={Hassan, H. M. and Fridovich, I.}, year={1979}, month={Mar}, pages={357–369} }
 @article{hassan_fridovich_1978, title={Regulation and Role of Superoxide Dismutase}, volume={6}, ISSN={0300-5127 1470-8752}, url={http://dx.doi.org/10.1042/bst0060356}, DOI={10.1042/bst0060356}, number={2}, journal={Biochemical Society Transactions}, publisher={Portland Press Ltd.}, author={Hassan, H. Moustafa and Fridovich, Irwin}, year={1978}, month={Apr}, pages={356–361} }
 @article{hassan_fridovich_1978, title={Regulation of the synthesis of catalase and peroxidase in Escherichia coli.}, volume={253}, ISSN={0021-9258}, url={http://dx.doi.org/10.1016/s0021-9258(19)46953-6}, DOI={10.1016/s0021-9258(19)46953-6}, abstractNote={Glucose suppresses the synthesis of catalase and of peroxidase in Escherichia coli. Exhaustion of the glucose present in a complex medium, or abrupt transfer of cells from a glucose-containing to a glucose-free medium, resulted in a sharp increase in both catalase and peroxidase. The glucose effect was diminished by CAMP, added to the suspending medium, thus identifying it as a catabolite repression. Aerobic growth of E. coli compared to anaerobic growth caused a large increase in catalase and peroxidase. This was not dependent upon either 02 or HzOz, since a similar induction was caused by the addition of NOs-, under anaerobic conditions. Mutants defective in the biosynthesis of ubiquinone were also defective in the ability to induce the synthesis of catalase and peroxidase. p-Hydroxybenzoate, which imparts phenotypic normality to these respiratory mutants, restored normal induction of catalase and peroxidase. Catalase and peroxidase were thus co-induced with the components of the respiratory chain. In all cases of induction of peroxidase and catalase, the increase in the former preceded that of the latter. Furthermore, the increase in peroxidase was transitory, whereas catalase increased to a more stable plateau. E. coli can generate two electrophoretically distinct catalases. One of these is constitutive and was present even in anaerobically grown or in glucoserepressed cells, whereas the other appeared only when the synthesis of catalase was derepressed in the absence of glucose by oxygen or nitrate.}, number={18}, journal={Journal of Biological Chemistry}, publisher={Elsevier BV}, author={Hassan, H.M. and Fridovich, I.}, year={1978}, month={Sep}, pages={6445–6450} }
 @misc{hassan_1978, title={Strategies of Microbial Life in Extreme Environment}, author={Hassan, H.}, year={1978}, month={Nov} }
 @article{hassan_fridovich_1978, title={Superoxide radical and the oxygen enhancement of the toxicity of paraquat in Escherichia coli.}, volume={253}, ISSN={0021-9258}, url={http://dx.doi.org/10.1016/s0021-9258(17)34373-9}, DOI={10.1016/s0021-9258(17)34373-9}, number={22}, journal={Journal of Biological Chemistry}, publisher={Elsevier BV}, author={Hassan, H.M. and Fridovich, I.}, year={1978}, month={Nov}, pages={8143–8148} }
 @article{hassan_pratt_1977, title={Biochemical and physiological properties of alkaline phosphatases in five isolates of marine bacteria}, volume={129}, ISSN={0021-9193 1098-5530}, url={http://dx.doi.org/10.1128/jb.129.3.1607-1612.1977}, DOI={10.1128/jb.129.3.1607-1612.1977}, abstractNote={The alkaline phosphatase activities of five unique isolates of marine bacteria were found to be associated with the periplasmic space; however, the enzymes from these isolates differed with respect to their repressibility, the apparent number of isoenzymes, the necessity for Mg2 for activity, and the conditions required for their release. With three of the isolates, the enzyme was released when cells that had been washed in 0.5 M NaCl were suspended in sucrose; however, with the other two isolates, one required the additional presence of tris(hydroxymethyl)aminomethane and the other required the presence of lysozyme and ethylenediaminetetraacetic acid. In two isolates the activity was constitutive, in two it was partially repressed, and in one it was completely repressed by inorganic phosphate. The repression of activity was associated with corresponding changes of activity bands as seen by acrylamide gel electrophoresis.}, number={3}, journal={Journal of Bacteriology}, publisher={American Society for Microbiology}, author={Hassan, H M and Pratt, D}, year={1977}, month={Mar}, pages={1607–1612} }
 @article{hassan_fridovich_1977, title={Enzymatic defenses against the toxicity of oxygen and of streptonigrin in Escherichia coli}, volume={129}, ISSN={0021-9193 1098-5530}, url={http://dx.doi.org/10.1128/jb.129.3.1574-1583.1977}, DOI={10.1128/jb.129.3.1574-1583.1977}, abstractNote={Anaerobically grown Escherichia coli K-12 contain only one superoxide dismutase and that is the iron-containing isozyme found in the periplasmic space. Exposure to oxygen caused the induction of a manganese-containing superoxide dismutase and of another, previously undescribed, superoxide dismutase, as well as of catalase and peroxidase. These inductions differed in their responsiveness towards oxygen. Thus the very low levels of oxygen present in deep, static, aerobic cultures were enough for nearly maximal induction of the manganese-superoxide dismutase. In contrast, induction of the new superoxide dismutase, catalase, and peroxidase required the much higher levels of oxygen achieved in vigorously agitated aerobic cultures. Anaerobically grown cells showed a much greater oxygen enhancement of the lethality of streptonigrin than did aerobically grown cells, in accord with the proposal that streptonigrin can serve as an intracellular source of superoxide. Anaerobically grown cells in which enzyme inductions were prevented by puromycin were damaged by exposure to air. This damage was evidenced both as a decline in viable cell count and as structural abnormalities evident under an electron microscope.}, number={3}, journal={Journal of Bacteriology}, publisher={American Society for Microbiology}, author={Hassan, H M and Fridovich, I}, year={1977}, month={Mar}, pages={1574–1583} }
 @article{hassan_fridovich_1977, title={Physiological function of superoxide dismutase in glucose-limited chemostat cultures of Escherichia coli}, volume={130}, ISSN={0021-9193 1098-5530}, url={http://dx.doi.org/10.1128/jb.130.2.805-811.1977}, DOI={10.1128/jb.130.2.805-811.1977}, abstractNote={Conditions for continuous culture of Escherichia coli K-12 His- Thi- under glucose limitation were established. Both the capacity for respiration, at D greater than 0.2/h, and specific activity of superoxide dismutase increased as a function of specific growth rate, whereas peroxidase and catalase were either invariant with or inversely related to this growth rate. The abrupt increase in the availability of glucose, as a means of elevating the growth rate, was followed by an increase in superoxide dismutase, which reached a plateau before there was a significant increase in the growth rate. Thus, an increase in superoxide dismutase appeared to be a prerequisite for an increase in the rate of growth. Cells that had higher levels of superoxide dismutase, because of varying specific growth rates, were more resistant to the toxicity of hyperbaric oxygen. Superoxide dismutase thus behaved like an essential defense against the toxicity of oxygen. Sensitivity towards streptonigrin increased with specific growth rate in the range of 0.09 to 0.25/h but decreased with further increases in the growth rate. Since this antibiotic has been shown to shunt electrons to oxygen, with concomitant production of O2-, these results indicated a progressive deficiency of reducing power at growth rates below 0.25/h and a surfeit of reducing power with progressively greater protection against O2- by superoxide dismutase at growth rates greater than 0.25/h.}, number={2}, journal={Journal of Bacteriology}, publisher={American Society for Microbiology}, author={Hassan, H M and Fridovich, I}, year={1977}, month={May}, pages={805–811} }
 @article{hassan_fridovich_1977, title={Regulation of superoxide dismutase synthesis in Escherichia coli: glucose effect}, volume={132}, ISSN={0021-9193 1098-5530}, url={http://dx.doi.org/10.1128/jb.132.2.505-510.1977}, DOI={10.1128/jb.132.2.505-510.1977}, abstractNote={Growth of Escherichia coli, based upon the fermentation of glucose, is associated with a low intracellular level of superoxide dismutase. Exhaustion of glucose, or depression of the pH due to accumulation of organic acids, causes these organisms to then obtain energy from the oxidative degradation of other substances present in a rich medium. This shift in metabolism is associated with a marked increase in the rate of synthesis of superoxide dismutase. Depression of the synthesis of superoxide dismutase by glucose is not due to catabolite repression since it is not eliminated by cyclic adenosine 3',5'-monophosphate and since alpha-methyl glucoside does not mimic the effect of glucose. Moreover, glucose itself no longer depresses superoxide dismutase synthesis when the pH has fallen low enough to cause a shift to a non-fermentative metabolism. It appears likely that superoxide dismutase is controlled directly or indirectly by the intracellular level of O2- and that glucose depressed the level of this enzyme because glucose metabolism is not associated with as rapid a production of O2- as is the metabolsim of many other substances. In accord with this view is the observation that paraquat, which can increase the rate of production of O2- by redox cycling, caused a rapid and marked increase in superoxide dismutase.}, number={2}, journal={Journal of Bacteriology}, publisher={American Society for Microbiology}, author={Hassan, H Moustafa and Fridovich, I}, year={1977}, month={Nov}, pages={505–510} }
 @article{hassan_fridovich_1977, title={Regulation of the synthesis of superoxide dismutase in Escherichia coli. Induction by methyl viologen.}, volume={252}, ISSN={0021-9258}, url={http://dx.doi.org/10.1016/s0021-9258(17)41019-2}, DOI={10.1016/s0021-9258(17)41019-2}, number={21}, journal={Journal of Biological Chemistry}, publisher={Elsevier BV}, author={Hassan, H.M. and Fridovich, I.}, year={1977}, month={Nov}, pages={7667–7672} }
 @article{hassan_1976, title={Diminution of outer membrane permeability by Mg2+ in a marine pseudomonad}, volume={125}, ISSN={0021-9193 1098-5530}, url={http://dx.doi.org/10.1128/jb.125.3.910-915.1976}, DOI={10.1128/jb.125.3.910-915.1976}, abstractNote={Intact cells of the marine pseudomonad MB-45, in the presence of optimal Mg2+, exhibited little alkaline phosphatase activity as judged by the hydrolysis of p-nitrophenylphosphate. Sonic extracts, in contrast, were rich in this activity. Removal of the loosely bound outer layer did not diminish this crypticity of alkaline phosphatase, but decreasing the concentration of Mg2+ in the suspending medium progressively exposed the alkaline phosphatase. Since MB-45 did not liberate alkaline phosphatase into the surrounding medium even in the absence of Mg2+ and since this enzyme is localized in the periplasmic space, it can be concluded that the crypticity was due to the exclusion of p-nitrophenylphosphate by the outer membrane. Mg2+ is apparently essential for the full expression of this limited permeability.}, number={3}, journal={Journal of Bacteriology}, publisher={American Society for Microbiology}, author={Hassan, H Moustafa}, year={1976}, month={Mar}, pages={910–915} }
 @inbook{hassan_belyea_hassan_1975, title={Characterization of methane production from poultry manure}, booktitle={Managing Livestock Wastes}, publisher={American Society of Agricultural Engineers}, author={Hassan, H.M. and Belyea, D.A. and Hassan, A.E.}, year={1975}, pages={244–247, 251} }
 @inbook{hassan_hassan_smith_1975, place={Michigan, US}, title={Energy recovery and feed production from poultry waste}, booktitle={Energy, Agriculture and Waste Management}, publisher={Ann Arbor Science Publishers Inc.}, author={Hassan, A.E. and Hassan, H.M. and Smith, N.}, editor={Jewell, W.J.Editor}, year={1975}, pages={289–305} }
 @article{hassan_macleod_1975, title={Kinetics of Na+-dependent K+ ion transport in a marine pseudomonad}, volume={121}, ISSN={0021-9193 1098-5530}, url={http://dx.doi.org/10.1128/jb.121.1.160-164.1975}, DOI={10.1128/jb.121.1.160-164.1975}, abstractNote={The effect of external Na plus concentration on the transport of K plus was studied using K plus-depleted cells of a marine pseudomonad. K plus transport was found to be a saturable process and requires Na plus. The initial rates for K plus transport over a range of external K plus concentrations were measured in suspensions containing various fixed concentrations of Na plus. Reciprocals of the initial rates for K plus transport were plotted against reciprocals of the external concentration of K plus or Na plus to yield two primary Lineweaver-Burk plots. The experimental data were found to fit bisubstrate enzyme kinetics, with a sequential type mechanism. However, the initial rate data did not allow distinction between ordered or random mechanisms. The results suggest that Na plus and K plus form a ternary complex with a specific K plus carrier molecule on the outer surface of the membrane prior to translocation and the release of K plus inside the cell.}, number={1}, journal={Journal of Bacteriology}, publisher={American Society for Microbiology}, author={Hassan, H M and MacLeod, R A}, year={1975}, month={Jan}, pages={160–164} }
 @article{ingram_hassan_1975, title={The resistance of Pseudomonas aeruginosa to chloramphenicol}, volume={21}, ISSN={0008-4166 1480-3275}, url={http://dx.doi.org/10.1139/m75-177}, DOI={10.1139/m75-177}, abstractNote={A strain of Pseudomonas aeruginosa, which was resistant to 400 μg/ml of chloramphenicol (CM), was isolated. The generation time of the resistant strain was the same in the presence or absence of CM and similar to that of the parent strain growing in the absence of chloramphenicol. Resistance is eliminated by treatment with acridine dyes, mitomycin C, and sodium dodecyl sulfate, suggesting that resistance may be expressed by a plasmid. The resistant strain does not produce the pigment pyocyanine and the addition of pyocyanine to this strain eliminates the resistance factor. A strain sensitive to CM was isolated. This strain does not produce the enzyme acetyl CoA: chloramphenicol transacetylase whereas the resistant strain does. The sensitive strain accumulates 14 C-CM at a greater rate and to a greater extent than the resistant strain grown in the presence of CM. The results suggest that the resistant strain inactivates CM by acetylation and, in addition, develops a "permeability" barrier towards chloramphenicol.}, number={8}, journal={Canadian Journal of Microbiology}, publisher={Canadian Science Publishing}, author={Ingram, J. M. and Hassan, H. Moustafa}, year={1975}, month={Aug}, pages={1185–1191} }
 @article{ismail_el salam_hassan_1973, title={Effect of milk solids concentration on buffalo and cow soft cheese}, volume={21}, journal={Alexandria Journal of Agricultural Research}, author={Ismail, A.A. and El Salam, N.A. and Hassan, H.M.}, year={1973}, pages={383–389} }
 @article{ismail_el salam_hassan_1973, title={Some technological aspects of buffalo and cow soft cheese}, volume={21}, journal={Alexandria Journal of Agricultural Research}, author={Ismail, A.A. and El Salam, N.A. and Hassan, H.M.}, year={1973}, pages={391–396} }
 @article{hassan_collins_1969, title={Effects of Selected Food Additives on Growth of Pseudomonas fragi}, volume={52}, ISSN={0022-0302}, url={http://dx.doi.org/10.3168/jds.s0022-0302(69)86557-4}, DOI={10.3168/jds.s0022-0302(69)86557-4}, abstractNote={Abstract Tests were made of inhibition of Pseudomonas fragi in lactose-yeast extract broth by the food additives chlortctraeycline, nisin, bacitracin, chloramphenicol, lysozyme, ethylenediaminetetraacetic acid (EDTA), nitrofurazone, propyl-p-hydroxybenzoate, sodium benzoate, and potassium sorbate. The additives that proved effective in broth were tested in skimmilk and half-and-half. Nisin, bacitracin, lysozyme, and nitrofurazone were ineffective in broth; chloramphenicol increased the lag period prior to development of turbidity but resulted in chloramphenicol-resistant populations; and EDTA inhibited the organism slightly in broth but not in skimmilk or half-and-half. Propyl-p-hydroxybenzoate, chlortetracycline, and a mixture of lysozyme and EDTA were effective in broth but not in skimmilk or half-and-half, a difference attributed to metal ions in dairy products that react with chlortetracycline and EDTA. Sodium benzoate retarded P. fragi in broth, but only at low pH. Potassium sorbate was ineffective at pH 6.5 in broth, but at pH 5.5 and 5.2 inhibited growth of P. fragi in broth, skimmilk, and half-and-half.}, number={3}, journal={Journal of Dairy Science}, publisher={American Dairy Science Association}, author={Hassan, H. Moustafa and Collins, E.B.}, year={1969}, month={Mar}, pages={335–340} }
 @article{hassan_collins_1969, title={Molar Growth Yield of Streptococcus faecalis on Pyruvate}, volume={97}, ISSN={0021-9193 1098-5530}, url={http://dx.doi.org/10.1128/jb.97.3.1496-1497.1969}, DOI={10.1128/jb.97.3.1496-1497.1969}, abstractNote={Y(pyruvate) was 17.3, similar to Y(arginine), for Streptococcus faecalis 6783 grown statically in a complex medium in 1 atm of air.}, number={3}, journal={Journal of Bacteriology}, publisher={American Society for Microbiology}, author={Hassan, H. Moustafa and Collins, E. B.}, year={1969}, month={Mar}, pages={1496–1497} }
 @article{collins_hassan_1969, title={Sensory and Shelf-Life Evaluations of Cottage Cheese Treated with Potassium Sorbate}, volume={52}, ISSN={0022-0302}, url={http://dx.doi.org/10.3168/jds.s0022-0302(69)86584-7}, DOI={10.3168/jds.s0022-0302(69)86584-7}, abstractNote={Abstract Cottage cheese samples containing 0.025 to 0.20% potassium sorbate were evaluated by as ensory panel of 18 judges, using the duo-trio test method or organoleptically in seven Cottage cheese plants. The samples were then stored at 4 or 7 C and evaluated for shelf-life. The panel did not significantly detect 0.10% or less of potassium sorbate in Cottage cheese by taste or odor. The minimum levels of potassium sorbate detected in the Cottage cheese plants were 0.10% (four plants), 0.05% (two plants), and 0.025% (one plant). Shelf-life was extended in some experiments by 0.05% potassium sorbate and in all experiments by 0.10%. These amounts of potassium sorbate retarded growth of bacteria that produced fruity and putrid odors and slime in Cottage cheese at refrigeration temperatures and bacteria that produced sourness and molds.}, number={4}, journal={Journal of Dairy Science}, publisher={American Dairy Science Association}, author={Collins, E.B. and Hassan, H. Moustafa}, year={1969}, month={Apr}, pages={439–442} }
 @article{hassan_collins_1968, title={Molar Growth Yields of Certain Lactic Acid Bacteria as Influenced by Autolysis}, volume={96}, ISSN={0021-9193 1098-5530}, url={http://dx.doi.org/10.1128/jb.96.1.117-125.1968}, DOI={10.1128/jb.96.1.117-125.1968}, abstractNote={Molar growth yields determined from batch cultures of Streptococcus diacetilactis and S. faecalis were appreciably greater at the peaks of maximal growth than after continued incubation and considerable autolysis. The higher molar growth yields were about equal to those determined in a continuous culture. Autolysis during logarithmic growth was minimal. The average Y value for adenosine triphosphate (ATP), determined by using limiting concentrations of glucose, galactose, lactose, and maltose for growing S. diacetilactis and limiting concentrations of glucose for growing S. lactis, S. cremoris , and S. faecalis , was 17.0. This is close to the Y (arginine) value of 17.8 determined with S. faecalis , but 62% greater than the generally accepted value of 10.5. Data are presented indicating that the often-used Y (ATP) value of 10.5 is erroneously low.}, number={1}, journal={Journal of Bacteriology}, publisher={American Society for Microbiology}, author={Hassan, H. Moustafa and Collins, E. B.}, year={1968}, month={Jul}, pages={117–125} }
 @article{hassan_collins_1968, title={Role of Galactose or Glucose-1-Phosphate in Preventing the Lysis of
            Streptococcus diacetilactis}, volume={95}, ISSN={0021-9193 1098-5530}, url={http://dx.doi.org/10.1128/jb.95.2.592-602.1968}, DOI={10.1128/jb.95.2.592-602.1968}, abstractNote={Cells of Streptococcus diacetilactis DRCI grown at 32 C in media containing glucose as the energy source were osmotically fragile and began to lyse immediately after growth was stopped (by the action of chloramphenicol or the exhaustion of glucose), unless they were then stabilized by hypertonic medium or spermine or by storage at low p H or low temperature, or both. In media containing excess glucose, with growth limited by exhaustion of some nutrient other than the energy source, the appearance of lysis was masked by the occurrence of a balance between lysis and synthesis. The osmotic fragility apparently resulted from inability of the organism to use glucose as an adequate precursor of galactosamine, and conditions of temperature and p H that promoted rapid growth on glucose were particularly conducive to the formation of cells that lysed readily. Growing the organism in media containing galactose, lactose, maltose, or glucose (at 17 C) as energy source resulted in the formation of cells that were resistant to lysis and richer in galactosamine than unstable cells formed on glucose at 32 C. The results indicate that the organism phosphorolyzes maltose to glucose plus β-glucose-1-phosphate, and suggest that it can use the β-glucose-1-phosphate in place of α-glucose-1-phosphate in the formation of cell materials.}, number={2}, journal={Journal of Bacteriology}, publisher={American Society for Microbiology}, author={Hassan, H. Moustafa and Collins, E. B.}, year={1968}, month={Feb}, pages={592–602} }