Phosphorus Physiology of the Marine Cyanobacterium Trichodesmium

Elizabeth D. Orchard, Ph.D., 2010
Sonya Dyhrman, Advisor

The marine diazotroph Trichodesmium is a major contributor to both primary production and nitrogen fixation in the tropical and subtropical oceans, which are often characterized by low phosphorus (P) concentrations.  P deficiency of Trichodesmium could limit growth, and constrain nitrogen fixation by this genus.  Therefore, this thesis examines various aspects of P metabolism in Trichodesmium and the extent to which P limits Trichodesmium in the ocean.  Chapter two examines the relative importance of Pi and DOP in Trichodesmium in the Sargasso Sea by measuring uptake rates and uptake kinetics of radio-labeled substrate analogs.  Chapter three confirms the presence of polyP in the Sargasso Sea populations, and is the first detection of polyP in an oligotrophic system.  Chapter four examines the regulation of several genes involved in P scavenging in cultures of Trichodesmium including an alkaline phosphatase (phoX).  Chapter five calibrates the expression of phoX to decreases in nitrogen fixation allowing the use of phoX expression as an indicator of P limitation in Trichodesmium, which was then used in the field. 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 limits nitrogen fixation in Trichodesmium.