Popendorf Kimberly J.

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Popendorf
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Kimberly J.
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  • Article
    Gradients in intact polar diacylglycerolipids across the Mediterranean Sea are related to phosphate availability
    (Copernicus Publications on behalf of the European Geosciences Union, 2011-12-20) Popendorf, Kimberly J. ; Tanaka, T. ; Pujo-Pay, M. ; Lagaria, A. ; Courties, C. ; Conan, P. ; Oriol, L. ; Sofen, L. E. ; Moutin, T. ; Van Mooy, Benjamin A. S.
    Intact polar membrane lipids compose a significant fraction of cellular material in plankton and their synthesis imposes a substantial constraint on planktonic nutrient requirements. As a part of the Biogeochemistry from the Oligotrophic to the Ultraoligotrophic Mediterranean (BOUM) cruise we examined the distribution of several classes of intact polar diacylglycerolipids (IP-DAGs) across the Mediterranean, and found that phospholipid concentration as a percent of total lipids correlated with phosphate concentration. In addition, the ratios of non-phosphorus lipids to phospholipids – sulfoquinovosyldiacylglycerol (SQDG) to phosphatidylglycerol (PG), and betaine lipids to phosphatidylcholine (PC) – were also found to increase from west to east across the Mediterranean. Additionally, microcosm incubations from across the Mediterranean were amended with phosphate and ammonium, and in the course of several days nutrient amendments elicited a shift in the ratios of IP-DAGs. These experiments were used to assess the relative contribution of community shifts and physiological response to the observed change in IP-DAGs across the Mediterranean. The ratio of SQDG to chlorophyll-a was also explored as an indicator of phytoplankton response to nitrogen availability. This study is the first to demonstrate the dynamic response of membrane lipid composition to changes in nutrients in a natural, mixed planktonic community.
  • Thesis
    Marine microbial intact polar diacylglycerolipids and their application in the study of nutrient stress and bacterial production
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2013-02) Popendorf, Kimberly J.
    Intact polar diacylglycerolipids (IP-DAGs) were used to study microbial dynamics in the surface ocean. IP-DAGs from surface ocean seawater were quantified using high performance liquid chromatography-mass spectrometry (HPLC-MS), after first developing a sensitive, high throughput molecular ion independent triple quadrupole MS method for quantification. Using this analytical technique I examined the distribution of the nine most abundant classes of IPDAGs across the Mediterranean, and found that phospholipids as a percent of total IP-DAGs correlated with phosphate concentration. Furthermore, phospholipids were a higher percent of total particulate phosphorus where phosphate was higher, ranging from 1-14%. Thus IP-DAGs can play not only a significant but also a dynamic role in defining planktonic nutrient needs and cellular C:N:P ratios in the environment. Additionally, microcosm incubations were amended with phosphate and ammonium, and in the course of several days this elicited a shift in the ratios of IP-DAGs. This study was the first to demonstrate the dynamic response of membrane lipid composition to changes in nutrients in a natural, mixed planktonic community, and indicated that the change in IP-DAG ratios in response to changing nutrients may be a useful indicator of microbial nutrient stress. In the surface waters of the western North Atlantic I used three experimental approaches to identify the microbial sources of the nine most abundant classes of IP-DAGs. Phytoplankton are the primary source of one class of sulfolipid, sulfoquinovosyldiacylglycerol, and one class of betaine lipid, diacylglyceryl-trimethyl-homoserine, while heterotrophic bacteria are the dominant source of the phospholipids phosphatidylglycerol and phosphatidylethanolamine. In regrowth experiments in the Sargasso Sea and the North Pacific I demonstrated that phospholipid specific production rate is representative of heterotrophic bacterial cell specific growth rate. I measured phospholipid specific production rate and bacterial production rate using uptake of 3H-leucine (3H-Leu) and 3H-thymidine (3H-TdR) across the North Atlantic, across the Mediterranean, and in the North Pacific subtropical gyre. I found that phospholipid specific production rates estimate heterotrophic bacterial cell specific growth rates that are on the order of 1 per day, an order of magnitude faster than cell specific growth rates suggested by uptake of 3H-Leu and 3H-TdR.
  • Article
    Growth and mortality of aerobic anoxygenic phototrophs in the North Pacific Subtropical Gyre
    (American Society for Microbiology, 2024-03-29) Koblizek, Michal ; Ferrera, Isabel ; Kolarova, Eva ; Duhamel, Solange ; Popendorf, Kimberly J. ; Gasol, Josep M. ; Van Mooy, Benjamin A. S.
    Aerobic anoxygenic phototrophic (AAP) bacteria harvest light energy using bacteriochlorophyll-containing reaction centers to supplement their mostly heterotrophic metabolism. While their abundance and growth have been intensively studied in coastal environments, much less is known about their activity in oligotrophic open ocean regions. Therefore, we combined in situ sampling in the North Pacific Subtropical Gyre, north of O'ahu island, Hawaii, with two manipulation experiments. Infra-red epifluorescence microscopy documented that AAP bacteria represented approximately 2% of total bacteria in the euphotic zone with the maximum abundance in the upper 50 m. They conducted active photosynthetic electron transport with maximum rates up to 50 electrons per reaction center per second. The in situ decline of bacteriochlorophyll concentration over the daylight period, an estimate of loss rates due to predation, indicated that the AAP bacteria in the upper 50 m of the water column turned over at rates of 0.75–0.90 d−1. This corresponded well with the specific growth rate determined in dilution experiments where AAP bacteria grew at a rate 1.05 ± 0.09 d−1. An amendment of inorganic nitrogen to obtain N:P = 32 resulted in a more than 10 times increase in AAP abundance over 6 days. The presented data document that AAP bacteria are an active part of the bacterioplankton community in the oligotrophic North Pacific Subtropical Gyre and that their growth was mostly controlled by nitrogen availability and grazing pressure.