Complementation analysis of Klebsiella pneumoniae mutants defective in nitrogen fixation.

A series of mutants defective in nitrogen fixation (nif) were isolated in Klebsiella pneumoniae strain M5a1. The nif mutations were either located on plasmid pRD1 or on the K. pneumoniae chromosome. A total of 37 plasmid mutants and 28 chromosomal mutants were employed in complementation tests using the acetylene reduction technique. Most mutants could be assigned to one of seven nif cistrons: nifA, nifB, nifD, nifE, nifF, nifH, and nifK. Complementation analysis of two nif deletion mutants confirmed transductional evidence that these strains carry nifB-A-F deletions. One deletion mutant had, in contrast to previous transductional analysis, a functional nifK cistron and presumably is deleted for nifB-A-F-E. Examination of the biochemical phenotype of several mutants suggests that the nifA product has a regulatory function, and nifK, nifD and nifH are most probably the structural genes for nitrogenase.