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 2010
Description:
Primary producers play a critical role in the oceanic food chain and the global cycling of
carbon. The marine diazotroph Trichodesmium is a major contributor to both primary
production and nitrogen fixation in the tropical and subtropical oceans. These regions are
often characterized by low phosphorus (P) concentrations, and P deficiency of
Trichodesmium could limit growth, and constrain nitrogen fixation by this genus. Three
key components of P metabolism in cyanobacteria include: inorganic phosphate (Pi)
uptake, dissolved organic phosphorus (DOP) hydrolysis, and polyphosphate (polyP)
biosynthesis and catabolism. These three pathways lay the foundation for the four
chapters that make up the body of this thesis. Chapter two examines the relative
importance of Pi and DOP in Trichodesmium in the Sargasso Sea by measuring uptake
rates and uptake kinetics of 33Pi and DOP (using alpha labeled adenosine-5’-triphosphate
33P-ATP as a model P ester compound). The in situ uptake rates suggest that the
contribution of P ester to total P uptake can be greater than 25% for Trichodesmium, and
therefore P esters are important for supplementing Trichodesmium’s P demand. Chapter
three confirms the presence of polyP in the Sargasso Sea populations. This is the first
detection of polyP in an oligotrophic system and may indicate micro-scale variability in
DIP or DOP supply. Chapter four examines the regulation of several genes involved in P
scavenging in cultures of Trichodesmium erythraeum IMS101: two copies of a high
affinity phosphate binding protein (pstS and sphX) and two putative alkaline
phosphatases (phoA and phoX). Chapter five calibrates the expression of phoX to
decreases in nitrogen fixation rate in Trichodesmium cultures allowing the use of phoX
expression as a molecular indicator of P limitation of nitrogen fixation. Detection of
phoX expression in the North Atlantic and South Pacific identified the extent and
magnitude of P limitation in these regions. Taken together this thesis provides new
insights into how Trichodesmium survives in low P environments, utilizes DOP, stores
polyP, and the extent to which P can limit nitrogen fixation by this genus.
Description:
I have been supported by the National Science
Foundation (grants OCE-0549794 and CCF-424599), the Environmental Protection
Agency (R-83041501-0) and the WHOI Academic Programs Office.
Keywords:
Primary productivity
;
Cyanobacteria
;
Atlantic Exploer (Ship) Cruise
;
Kilo Moana (Ship) Cruise
Repository Name:
Woods Hole Open Access Server
Type:
Thesis
Format:
application/pdf
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