Genetic Analysis of Nitrogen Fixation in Anabaena Variabilis

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Nitrogen fixation, the reduction of atmospheric dinitrogen to ammonium by the enzyme nitrogenase, is repressed by fixed nitrogen and, because all nitrogenases are oxygen labile, by oxygen. Cyanobacteria of the genus Anabaena have specialized cells called heterocysts whose function is nitrogen fixation. Anabaena variabilis has three different nitrogenases; a V-dependent nitrogenase (vnf) and two Mo-dependent nitrogenases, one that functions under aerobic conditions (nif1) and one that functions only under strictly anaerobic conditions (nif2). The nitrogenase genes are tightly regulated; however, very little is known about their regulation. An understanding of nitrogenase gene regulation in A. variabilis will broaden our understanding of mechanisms of prokaryotic gene regulation. The nitrogenase genes in A. variabilis are regulated at many levels including nitrogen deprivation, oxygen tension, metal availability, and heterocyst development. The goal of the proposed research is to identify the regulatory circuits that control the nitrogenase genes that function under aerobic conditions in heterocysts of A. variabilis. The aims are to characterize the regions of the nitrogenase genes that are essential for regulated expression in heterocysts and to identify the proteins responsible for regulation. The broader impact of this project includes the integration of research with both undergraduate and graduate education, including the development of an undergraduate research course that will allow each student in the course to make a substantial contribution to this research project.