U.S.-Brazil Cooperative Research: Genetic Analysis of Nitrogen Fixation in Acetobacter diazotrophicus, an Endophyte of Sugar Cane

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9302788 Kennedy This U.S.-Brazil Program award will support the collaboration of Christina Kennedy of the University of Arizona and Johanna Dobereiner of EMBRAPA in Rio de Janeiro, Brazil. The project aims to isolate and mutate genes of Azobacter diazotrophicus necessary for nitrogenase enzyme activity. Nitrogen-fixing bacteria have been isolated from sugar cane varieties in Brazil in which up to 70 percent of total plant nitrogen comes from atmospheric nitrogen (dinitrogen). The major organism isolated, A. diazotrophicus, is an endophyte thought to be responsible for the fixation of dinitrogen and transfer of products to the plant system. The researchers will use mutants unable to fix nitrogen to prove or disprove a role for this species in providing fixed nitrogen in sugar cane. They will also characterize genes involved in bacterial responses to environmental factors such as ammonia and oxygen that control nitrogenase biosynthesis. Strategies to increase amounts of fixed nitrogen provided to plants will be applied to construct strains that produce nitrogenase in the presence of ammonia or have increased tolerance to oxygen. The U.S. side has expertise in the genetics of nitrogen-fixing bacteria. The Brazilian laboratory is where A. diazotrophicus was identified and its colonization of plants is being studied. Both sides will benefit from establishing the significance of a novel and potentially important nitrogen-fixing bacterial species. ***