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Ph.D. Kim Popendorf Lamont-­‐Doherty Earth Observatory Biology and Paleo Environment [email protected] Microbial phosphorus dynamics: uptake, allocation, and phospholipid turnover rates Phosphorus is a limiting macronutrient for biological productivity in many areas of the ocean, making its utilization an important lever in controlling the role of microbes in global biogeochemical cycles. Using cell sorting flow cytometry, we assessed the relative role of picophytoplankton groups (Synechococcus, Prochlorococcus, and pigmented picoeukaryotes) and heterotrophic bacteria in phosphorus uptake in the oligotrophic Gulf of Mexico, tracing the uptake of both dissolved inorganic phosphorus (DIP) and dissolved organic phosphorus (DOP) using radioisotope tracer incubations. Coupling this with preparative liquid chromatography, we assessed the relative cellular allocation of phosphorus into microbial membrane phospholipids. Prior work has suggested that these membrane lipids may be one of the most variable cellular pools of phosphorus across different picoplankton groups, and indeed we demonstrated that the allocation of phosphorus into phospholipids varies significantly and systematically across picoplankton groups. Building from this variation in microbial phospholipid production, we explored the utility of phospholipid turnover rates as a novel tool for measuring heterotrophic bacterial production rate in the oligotrophic open ocean, and show that bacterial production rates may be more rapid than the canonical paradigm. Princeton University Environmental Geology and Geochemistry Seminar 13 March 2014