Comparative studies have revealed the presence of a large number of genes that are associated with nitrogen fixation in the obligate aerobe Azotobacter vinelandii but are not present in the facultative anaerobe Klebsiella pneumoniae. A number of these nif-associated genes have also been discovered in Rhodobacter capsulatus, Anabaena, and Bradyrhizobium japonicum and they are, therefore, likely to be involved in nitrogen fixation under aerobic or microaerobic conditions. In this project we will attempt to isolate and characterize all of the remaining nif-associated genes from A. vinelandii. Also, experiments designed to determine the physiological function of each nif-associated gene product will be performed. Our approach will involve the isolation of a set of mutant strains, each individually deleted for a specific nif-associated gene. Also, deletions within nif-associated gene products will be placed in combination with other characterized nif-specific mutations. Such specifically constructed strains will be examined for; a) diazotrophic growth abilities, b) accumulation of nif-specific mRNAs, c) accumulation of nif-specific gene products, d) nitrogenase component protein specific activities, e) response to molybdenum deprivation, and f) ability to recover from or cope with various diazotrophic growth conditions.
