@article{skelton_burkholder_parrow_2009, title={Axenic Culture of the Heterotrophic Dinoflagellate Pfiesteria shumwayae in a Semi-Defined Medium}, volume={56}, ISSN={["1550-7408"]}, DOI={10.1111/j.1550-7408.2008.00368.x}, abstractNote={ABSTRACT.  A semi‐defined, biphasic culture medium was developed that supported the axenic growth of three strains of the heterotrophic dinoflagellate Pfiesteria shumwayae. Maximum cell yields and division rates in the semi‐defined medium ranged from 0.1 × 105 to 4.0 × 105 cells/ml and 0.5 to 1.7 divisions/day, respectively, and depended on the concentration of the major components in the medium as well as the P. shumwayae strain. The medium contained high concentrations of certain dissolved and particulate organic compounds, including amino acids and lipids. Pfiesteria shumwayae flagellated cells were attracted to insoluble lipids present in the medium and appeared to feed on the lipid particles, suggesting that phagocytosis may be required for growth in axenic culture. Development of a semi‐defined medium represents significant progress toward a completely defined axenic culture medium and subsequent determination of the biochemical requirements of P. shumwayae, needed to advance understanding of the nutritional ecology of this species. Further, this medium provides an economical, simplified method for generating high cell densities of P. shumwayae in axenic culture that will facilitate controlled investigations on the physiology and biochemistry of this heterotrophic dinoflagellate.}, number={1}, journal={JOURNAL OF EUKARYOTIC MICROBIOLOGY}, author={Skelton, Hayley M. and Burkholder, Joann M. and Parrow, Matthew W.}, year={2009}, pages={73–82} }
 @article{glibert_burkholder_kana_alexander_skelton_shilling_2009, title={Grazing by Karenia brevis on Synechococcus enhances its growth rate and may help to sustain blooms}, volume={55}, ISSN={["1616-1564"]}, DOI={10.3354/ame01279}, abstractNote={Grazing rates of Karenia brevis Clones CCMP2228 and CCMP2229 were determined in laboratory experiments using Synechococcus sp. Clone CCMP1768 as food. Growth (days to weeks) and uptake rates (hours to days) were assessed. In the growth experiments, K. brevis, previously depleted in nitrogen (N), was grown at 2 light intensities in the presence of varying concentrations of Synechococcus. Under high irradiance (300 µmol photons m -2 s -1 ; 14 h light:10 h dark cycle), expo- nential growth rates approximated those of phototrophic growth without Synechococcus (0.26 to 0.35 d -1 ). At this irradiance, K. brevis cells in all treatments grew for about 10 d. Under lower irradi- ance (43 µmol photons m -2 s -1 ), exponential growth rates of K. brevis cells varied with the enrichment level of Synechococcus, with rates under the highest Synechococcus enrichment level being nearly twice (0.58 d -1 ) those observed for the high irradiance treatments. Short-term uptake experiments (3 experiments, 2 clones) were done to examine the N-specific rates of grazing of 15 N-labeled Syne- chococcus. N-specific rates of grazing ranged from 9.28 × 10 -4 h -1 to 1.22 × 10 -2 h -1 and varied with the relative proportion of Synechococcus:K. brevis. These rates represent a range of 0.026 to 2.15 pmol-N K. brevis -1 d -1 , or 0.96 to 83.8 Synechococcus K. brevis -1 h -1 . Evidence of Synechococcus inside K. brevis was provided by confocal microscopy. Grazing by K. brevis thus enhances the range of nutritional substrates available to meet its growth requirements, and may play a substantial role in sustaining natural populations in inorganic N-poor waters.}, number={1}, journal={AQUATIC MICROBIAL ECOLOGY}, author={Glibert, Patricia M. and Burkholder, JoAnn M. and Kana, Todd M. and Alexander, Jeffrey and Skelton, Hayley and Shilling, Carol}, year={2009}, pages={17–30} }
 @article{skelton_burkholder_parrow_2008, title={AXENIC CULTIVATION OF THE HETEROTROPHIC DINOFLAGELLATE PFIESTERIA SHUMWAYAE AND OBSERVATIONS ON FEEDING BEHAVIOR}, volume={44}, ISSN={["1529-8817"]}, DOI={10.1111/j.1529-8817.2008.00601.x}, abstractNote={ Pfiesteria shumwayae Glasgow et J. M. Burkh. [=Pseudopfiesteria shumwayae (Glasgow et J. M. Burkh.) Litaker, Steid., P. L. Mason, Shields et P. A. Tester] is a heterotrophic dinoflagellate commonly found in temperate, estuarine waters. P. shumwayae can feed on other protists, fish, and invertebrates, but research on the biochemical requirements of this species has been restricted by the lack of axenic cultures. An undefined, biphasic culture medium was formulated that supported the axenic growth of two of three strains of P. shumwayae. The medium contained chicken egg yolk as a major component. Successful growth depended on the method used to sterilize the medium, and maximum cell yields (104 · mL−1) were similar to those attained in previous research when P. shumwayae was cultured with living fish or microalgae. Additionally, P. shumwayae flagellate cells ingested particles present in the biphasic medium, allowing detailed observations of feeding behavior. This research is an initial step toward a chemically defined axenic culture medium and determination of P. shumwayae metabolic requirements.}, number={6}, journal={JOURNAL OF PHYCOLOGY}, author={Skelton, Hayley M. and Burkholder, JoAnn M. and Parrow, Matthew W.}, year={2008}, month={Dec}, pages={1614–1624} }
 @misc{burkholder_glibert_skelton_2008, title={Mixotrophy, a major mode of nutrition for harmful algal species in eutrophic waters}, volume={8}, ISSN={["1878-1470"]}, DOI={10.1016/j.hal.2008.08.010}, abstractNote={Historically most harmful algal species (HAS) have been thought to be strictly phototrophic. Mixotrophy, the use of phototrophy and heterotrophy in combination, has been emphasized as operative mainly in nutrient-poor habitats as a mechanism for augmenting nutrient supplies. Here we examine an alternate premise, that many harmful algae which thrive in eutrophic habitats are mixotrophs that respond both directly to nutrient inputs, and indirectly through high abundance of bacterial and algal prey that are stimulated by the elevated nutrients. From review and synthesis of the available data, mixotrophy occurs in all HAS examined thus far in the organic substrate- and prey-rich habitats of eutrophic estuarine and marine coastal waters. Where data are available comparing phototrophy versus mixotrophy, mixotrophy in eutrophic habitats generally is significant in nutrient acquisition and growth of HAS and, therefore, likely important in the development and maintenance of their blooms. In eutrophic habitats phagotrophic mixotrophs, in particular, have been shown to attain higher growth than when in phototrophic mode. Yet for many HAS, quantitative data about the role of mixotrophy in nutrition, growth, and blooms are lacking, especially relating laboratory information to natural field assemblages, so that the relative importance of photosynthesis, dissolved organic nutrients, and ingestion of prey largely remain unknown. Research is needed to assess simultaneously the roles of phototrophy, osmotrophy and phagotrophy in the nutritional ecology of HAS in eutrophic habitats, spanning bloom initiation, development and senescence. From these data, models that include the role of mixotrophy can be developed to gain more realistic insights about the nutritional factors that control harmful algae in eutrophic waters, and to strengthen predictive capability in predicting their blooms. An overall forecast that can be tested, as well, is that harmful mixotrophic algae will become more abundant as their food supplies increase in many estuaries and coastal waters that are sustaining chronic, increasing cultural eutrophication.}, number={1}, journal={HARMFUL ALGAE}, author={Burkholder, JoAann M. and Glibert, Patricia M. and Skelton, Hayley M.}, year={2008}, month={Dec}, pages={77–93} }
 @article{skelton_parrow_burkholder_2006, title={Phosphatase activity in the heterotrophic dinoflagellate Pfiesteria shumwayae}, volume={5}, ISSN={["1878-1470"]}, DOI={10.1016/j.hal.2006.04.010}, abstractNote={The ELF-97 phosphatase substrate was used to examine phosphatase activity in four strains of the estuarine heterotrophic dinoflagellate, Pfiesteria shumwayae. Acid and alkaline phosphatase activities also were evaluated at different pH values using bulk colorimetric methods. Intracellular phosphatase activity was demonstrated in P. shumwayae cells that were actively feeding on a fish cell line and in food limited cells that had not fed on fish cells for 3 days. All strains, whether actively feeding or food limited showed similar phosphatase activities. P. shumwayae cells feeding on fish cells showed ELF-97 activity near, or surrounding, the food vacuole. Relatively small, spherical ELF-97 deposits were also observed in the cytoplasm and sometimes near the plasma membrane. ELF-97 fluorescence was highly variable among cells, likely reflecting different stages in digestion and related metabolic processes. The location of enzyme activity and supporting colorimetric measurements suggest that, as in other heterotrophic protists, acid phosphatases predominate in P. shumwayae and have a general catabolic function.}, number={4}, journal={HARMFUL ALGAE}, author={Skelton, Hayley M. and Parrow, Matthew W. and Burkholder, JoAnn M.}, year={2006}, month={Sep}, pages={395–406} }