Publication Date:
2022-05-25
Description:
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2013
Description:
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.
Description:
This research was supported by a National Science Foundation Graduate Research Fellowship, a
National Defense Science and Engineering Graduate Fellowship, and grants from the U.S. Office
of Naval Research (N00014-09-1-0091 and N00014-06-1-0134) and the U.S. National Science
Foundation (OCE-1031143, OCE-1029687, and OCE-0646944).
Keywords:
Microbial ecology
;
Microbiological chemistry
;
Atlantic Exploer (Ship) Cruise BV39
;
Oceanus (Ship : 1975-) Cruise OC443
;
L'Atalante (Ship) BOUM Cruise
;
Kilo Moana (Ship) Cruise KM1013
Repository Name:
Woods Hole Open Access Server
Type:
Thesis
Format:
application/pdf
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