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Barry Sherr
Professor, College of Oceanic and Atmospheric Sciences
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RESEARCH:
Heterotrophic microbes are extraoridnarily important in temrs of biomass and activity in the sea, but there is much we do not understand about these organisms and their roles in marine biogeochemistry. We are interested in the physiology and ecology of marine microbes, including both bacteria and protists. Our current research focuses on cell-specific metabolic activity of marine bacterioplankton. This project is designed to resolve a long-standing controversy concerning what fractions of marine bacterial cells are metabolically active and growing, alive but not growing, or actually dead. We are using a combination of microautoradiography, flow cytometry, and fluorochrome-based assays to examine physiologically distinct categories of bacteria. The categories include bacterial cells with high DNA versus low-DNA content using SYBR Green stain, and bacteria with highly active or inactive electron transport systems using CTC redox reagent. Cell-specific metabolic activity will be quantitatively assessed via incorporation of radiolabeled substrates such as amino acids. Flow cytometric sorting of specific categories of stained cells will allow us to evaluate relative activity among the various physiological states of marine bacteria. In addition, we plan to phylogenetically identify highly metabolically active cells in marine bacterial assemblages via molecular genetic analysis of high-DNA and ETC-active cells separated by cytometric sorting.
We are also interested in trophic interactions between phagotrophic protists and microbial prey in marine planktonic food webs. Phagotrophic protists are important grazers of heterotrophic bacteria, phototrophic bacteria including coccoid cyanobacteria and prochlorophytes, and eukaryotic phototrophs. A longer-range goal is phylogenetic identification of specific groups of marine heterotrophic protists, and using molecular probes to aid in the analysis of the growth and feed rates of identified protist groups in planktonic ecosystems.