@article{almaraz_whitaker_andrews_duckworth_2017, title={Assessing Biomineral Formation by Iron-oxidizing Bacteria in a Circumneutral Creek}, volume={160}, ISSN={["1936-704X"]}, DOI={10.1111/j.1936-704x.2017.03240.x}, abstractNote={AbstractIron oxidizing bacteria and environmental conditions influence the formation of iron biominerals in aquatic environments. This 10‐week Research Experience for Undergraduates (REU) study focused on elucidating how water chemistry and iron oxidizing bacteria affect the formation of iron oxides in creeks with circumneutral pH. Two locations, each with multiple microenvironments containing abundant iron oxide deposits, were studied. Water chemistry was assessed via both in situ and laboratory analysis over a 5‐week period, revealing correlations between aqueous components that indicate differing groundwater sources may feed nearby discharge points. Microscopy of iron oxide deposits reveals morphologies consistent with the presence of iron oxidizing bacteria. Although efforts to isolate iron oxidizing bacteria did not produce pure cultures, 16S ribosomal DNA analysis also suggests the presence of iron oxidizing bacteria in these sites. Taken together, these results show the diversity of iron oxide forming microenvironments in spatially collocated sites, which may result in unique formations of iron oxide structures, microbial communities, and aqueous chemical cycling.}, number={1}, journal={JOURNAL OF CONTEMPORARY WATER RESEARCH & EDUCATION}, author={Almaraz, Nohemi and Whitaker, Andrew H. and Andrews, Megan Y. and Duckworth, Owen W.}, year={2017}, month={Apr}, pages={60–71} }
 @article{duckworth_andrews_cubeta_grunden_ojiambo_2017, title={Revisiting Graduate Student Training to Address Agricultural and Environmental Societal Challenges}, volume={2}, ISSN={2471-9625}, url={http://dx.doi.org/10.2134/ael2017.06.0019}, DOI={10.2134/ael2017.06.0019}, abstractNote={Core Ideas
Society is faced with daunting environmental and agricultural challenges.
There is a pressing need for multidisciplinary teams of collaborative scientists.
Novel graduate educational models may be needed to train students to address grand challenges.
An example of illustrating the model through microbiome science of plants and soil is presented.
Society and the higher education system are faced with daunting challenges associated with supplying food, energy, and water to a growing population while maintaining environmental quality and preserving natural resources. Too often, the higher education system does not facilitate collaborative immersion required to foster concerted multidisciplinary efforts needed to address societal grand challenges. In this commentary, we present an innovative model of cohort education, which equips graduate students with core skills and enables collaborative dissertation research among students. In addition, we provide an example of a program aimed at understanding the plant–soil microbiome, a critical research area that may yield significant advances in plant health and productivity.}, number={1}, journal={Agricultural & Environmental Letters}, publisher={Wiley}, author={Duckworth, Owen W. and Andrews, Megan Y. and Cubeta, Marc A. and Grunden, Amy M. and Ojiambo, Peter S.}, year={2017}, pages={170019} }
 @article{andrews_duckworth_2016, title={A universal assay for the detection of siderophore activity in natural waters}, volume={29}, ISSN={["1572-8773"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84994285887&partnerID=MN8TOARS}, DOI={10.1007/s10534-016-9979-4}, abstractNote={Siderophores, a family of biogenic metal chelating agents, play critical roles in the biogeochemical cycling of Fe and other metals by facilitating their solubilization and uptake in circumneutral to alkaline oxic environments. However, because of their small concentrations (ca. nM) and large number of molecular structures, siderophore detection and quantification in environmental samples requires specialized equipment and expertise, and often requires pre-concentration of samples, which may introduce significant bias. The "universal" CAS assay, which was originally designed for use in bacterial cultures, quantifies the iron chelating function of a pool of siderophores but only at concentrations (>2 µM) well above the concentrations estimated to be present in marine, freshwater, and soil samples. In this manuscript, we present a high sensitivity modification of this universal assay (HS-CAS) suitable for detecting and quantifying siderophore activity in the nM concentration range, allowing for direct quantitation of siderophore reactivity in transparent aqueous samples.}, number={6}, journal={BIOMETALS}, author={Andrews, Megan Y. and Duckworth, Owen}, year={2016}, month={Dec}, pages={1085–1095} }
 @article{duckworth_rivera_gardner_andrews_santelli_polizzotto_2017, title={Morphology, structure, and metal binding mechanisms of biogenic manganese oxides in a superfund site treatment system}, volume={19}, ISSN={["2050-7895"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85010739340&partnerID=MN8TOARS}, DOI={10.1039/c6em00525j}, abstractNote={Manganese oxides, which may be biogenically produced in both pristine and contaminated environments, have a large affinity for many trace metals.}, number={1}, journal={ENVIRONMENTAL SCIENCE-PROCESSES & IMPACTS}, author={Duckworth, O. W. and Rivera, N. A. and Gardner, T. G. and Andrews, M. Y. and Santelli, C. M. and Polizzotto, M. L.}, year={2017}, month={Jan}, pages={50–58} }
 @article{andrews_santelli_duckworth_2016, title={Layer plate CAS assay for the quantitation of siderophore production and determination of exudation patterns for fungi}, volume={121}, ISSN={["1872-8359"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84953386448&partnerID=MN8TOARS}, DOI={10.1016/j.mimet.2015.12.012}, abstractNote={The chrome azurol S (CAS) assay measures the chelating activity of siderophores, but its application (especially to fungi) is limited by toxicity issues. In this note, we describe a modified version of the CAS assay that is suitable for quantifying siderophore exudation for microorganisms, including fungi.}, journal={JOURNAL OF MICROBIOLOGICAL METHODS}, author={Andrews, Megan Y. and Santelli, Cara M. and Duckworth, Owen W.}, year={2016}, month={Feb}, pages={41–43} }
 @article{quirk_andrews_leake_banwart_beerling_2014, title={Ectomycorrhizal fungi and past high CO2 atmospheres enhance mineral weathering through increased below-ground carbon-energy fluxes}, volume={10}, ISSN={["1744-957X"]}, DOI={10.1098/rsbl.2014.0375}, abstractNote={Field studies indicate an intensification of mineral weathering with advancement from arbuscular mycorrhizal (AM) to later-evolving ectomycorrhizal (EM) fungal partners of gymnosperm and angiosperm trees. We test the hypothesis that this intensification is driven by increasing photosynthate carbon allocation to mycorrhizal mycelial networks using14CO2-tracer experiments with representative tree–fungus mycorrhizal partnerships. Trees were grown in either a simulated past CO2atmosphere (1500 ppm)—under which EM fungi evolved—or near-current CO2(450 ppm). We report a direct linkage between photosynthate-energy fluxes from trees to EM and AM mycorrhizal mycelium and rates of calcium silicate weathering. Calcium dissolution rates halved for both AM and EM trees as CO2fell from 1500 to 450 ppm, but silicate weathering by AM trees at high CO2approached rates for EM trees at near-current CO2. Our findings provide mechanistic insights into the involvement of EM-associating forest trees in strengthening biological feedbacks on the geochemical carbon cycle that regulate atmospheric CO2over millions of years.}, number={7}, journal={BIOLOGY LETTERS}, author={Quirk, Joe and Andrews, Megan Y. and Leake, Jonathan R. and Banwart, Steve A. and Beerling, David J.}, year={2014}, month={Jul} }
 @article{duckworth_akafia_andrews_bargar_2014, title={Siderophore-promoted dissolution of chromium from hydroxide minerals}, volume={16}, ISSN={["2050-7895"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84901660425&partnerID=MN8TOARS}, DOI={10.1039/c3em00717k}, abstractNote={Biomolecules have significant impacts on the fate and transport of contaminant metals in soils and natural waters. Siderophores, Fe(iii)-binding agents that are exuded by microbes and plants, may form strong complexes with and promote the dissolution of contaminant metal ions, such as Co(iii), U(iv), or Pu(iv). Although aqueous Cr(iii)-siderophore complexes have been recognized in the laboratory setting for almost 40 years, few studies have explored interactions of siderophores with Cr-bearing minerals or considered their impacts on environmental chemistry. To better understand the possible effects of siderophores on chromium mobility, we conducted a series of dissolution experiments to quantify the dissolution rates of Cr(iii)(OH)3 in the presence of hydroxamate, catecholate, and α-hydroxycarboxylate siderophores over a range of environmentally relevant pH values. At pH = 5, dissolution rates in the presence of siderophores are similar to control experiments, suggesting a predominantly proton-promoted dissolution mechanism. At pH = 8, the sorption of the siderophores desferrioxamine B and rhizoferrin can be modeled by using Langmuir isotherms. The dissolution rates for these siderophores are proportional to the surface concentrations of sorbed siderophore, and extended X-ray absorption fine structure spectra of dissolution products indicates the formation of Cr(iii)HDFOB(+) and Cr(iii)rhizoferrin(3-) complexes, suggesting a ligand-promoted dissolution mechanism at alkaline pH. Because siderophores promote Cr(iii)(OH)3 dissolution at rates similar in magnitude to those of iron hydroxides and the resulting Cr(iii)-siderophore complexes may be persistent in solution, siderophores could potentially contribute to the mobilization of Cr in soils and sediments where it is abundant due to geological or anthropogenic sources.}, number={6}, journal={ENVIRONMENTAL SCIENCE-PROCESSES & IMPACTS}, author={Duckworth, Owen W. and Akafia, Martin M. and Andrews, Megan Y. and Bargar, John R.}, year={2014}, pages={1348–1359} }