Regulation of nitrogenase synthesis by Klebsiella pneumoniae.

The synthesis of the nitrogenase system in N2-fixing bacteria is repressed when the organisms are grown on NH4+-N. It has not been unequivocally determined, however, if N2 is necessary for induction in NH4+-deficient cultures. Previous experiments with Klebsiella pneumoniae, Azotobacter vinelandii, Clostridium pasteurianum, and Rhodospirillum rubrum have been inconclusive owing to inadequacy of the methods, primarily the presence of N2 as a contaminant in the gases used. Results of experiments described in this paper using cultures of K. pneumoniae M5a1 grown under both limited N2 and in its apparent absence indicate that the control of nitrogenase is most likely through simple repression by NH4+ or by an incorporation product, e.g., glutamine.