Molecular Biology of Nitrogenase Genes in Trichodesmium, A Marine Nonheterocystous Cyanobacterium

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Trichodesmium is a species of photosynthetic bacteria , a cyanobacterium, which forms large concentrations in the surface waters of the open ocean. It posesses the ability to fix atmospheric nitrogen unlike most of the other phytoplankton which depend upon the dissolved forms of nitrogen in seawater , eg. nitrate, for uptake into the cell for subsequent growth. At times, this species forms dense blooms which may be extremely important in transient rates of new production in the ocean. Since the discovery of nitrogen fixation in association with Trichodesmium, many studies have attempted to characterize the nitrogen fixation activity and physiology of the species. However, the mechanisms of nitrogen fixation are still not understood. The enzyme nitrogenase which catalyzes the reduction of dinitrogen to ammonium is rapidly inactivated by oxygen. Therefore these organisms which live in the high oxygen zone of the surface waters must somehow protect their nitrogenase from the oxygen that they themselves generate during photosynthesis. Dr. Zehr focuses his work on two major questions: 1) how does Trichodesmium fix nitrogen and evolve oxygen simultaneously, and 2) does Trichodesmium posess a unique or alternative nitrogenase system that allows it to synthesize active nitrogenase in waters depleted of micronutrients such as molybdenum. The work identifies unique characteristics of the nitrogenase genes in the species using molecular techniques to construct a genomic library to characterize the organization of the gene. Probes and antibodies are to be prepared to study the expression of the genes in natural populations and cultures.