Mutants That Produce Nitrogenase in the Presence of Ammonia

Mutants of Azotobacter vinelandii that fix N(2) in the presence of excess NH(4) (+) have been isolated. A mutant that was unable to synthesize component I and component II of nitrogenase was spontaneously reverted to the N(2)-fixing phenotype. Of 21 revertants picked, 7 revertants were not as sensitive as the wild type to repression. A derepressed mutant is as sensitive as the wild type to growth inhibition by 2-methylalanine in the presence of glucose.