Complementation analysis and characterization of the nitrogen fixation genes, nifH, nifC and nifJ in Klebsiella pneumoniae.

Complementation tests were performed with various nif mutations for delineating the nif genes. The nif-/nif- heterogenotes were constructed by transferring nif plasmid mutant PRD-nif- from E. coli Jc5466 to various Klebsiella pneumoniae nif- recipients. In addition to those nif genes previously reported elsewhere, a new essential gene for nitrogen fixation, nifC was identified. According to the P1-transduction and three factor reciprocal crosses, nifC was tentatively mapped between nifH and nifJ in the chromsome. The order of nif genes obtained was hisD, nifQ, nifB, nifA, nifL, nifF nifM, nifV, nifS, nifU, nifN, nifE, nifK, nifD, nifH, nifC and nifJ. The examination of the biochemical phenotypes of the nif genes suggests that nifC may be concerned with the synthesis or activation of the iron molybdenum cofactor nitrogenase, nifH, besides coding for the structure of nitrogen reductase may also exert a function on the synthesis of nitrogenase, and nifJ presumably is required to turn on the expression of nifK (D), nifH or nifF.