RUI: Regulation of Nitrogenases in the Cyanobacterium Anabaena Variabilis

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Filamentous cyanobacteria are unique microorganisms which can produce energy by plant type photosynthesis and reduce atmospheric nitrogen by nitrogen fixation. Nitrogen fixation is severely inhibited by the oxygen produced by photosynthesis; hence, these two incompatible metabolic processes are spatially separated. Photosynthesis occurs in vegetative cells and nitrogen fixation occurs in heterocysts. Heterocysts are terminally differentiated cells which arise in a semi-regular pattern in a filament in response to starvation for fixed nitrogen. Nitrogenase is the enzyme complex, localized in heterocysts, that is responsible for the reduction of atmospheric nitrogen to ammonia. The PI is interested in the regulatory signals which control expression of nitrogenase genes in heterocysts. She has recently found a new set of genes that appear to code for a second nitrogenase in Anabaena variabilis. This second nitrogenase is genetically similar to a vanadium- dependent nitrogenase characterized in two species of Azotobacter. It does not appear to be another copy of the conventional nitrogenase of Anabaena. The PI proposes to analyze the two nitrogenase genes of Anabaena variabilis in an attempt to identify regulatory sites and regulatory gene that are important in developmental control of expression of nitrogenases.