IDENTIFICATION AND SEQUENCE OF A NIFJ-LIKE GENE IN RHODOSPIRILLUM-RUBRUM - PARTIAL CHARACTERIZATION OF A MUTANT UNAFFECTED IN NITROGEN-FIXATION

A nifJ-like gene was identified in the photosynthetic purple non-sulph ur bacterium Rhodospirillum rubrum, A DNA segment hybridizing to Klebs iella pneumoniae nifJ was isolated, the gene was inactivated, and a mu tant strain, SNJ-1, was constructed by allele replacement. The mutatio n was confirmed by DNA sequencing, Northern blotting and by the lack o f pyruvate oxidoreductase activity. This is the first report of a nifJ -like gene in photosynthetic bacteria. Unexpectedly, SNJ-1 was capable of nitrogen fixation, and growth was similar to the wild-type strain under all conditions investigated. Therefore, this is also the first d emonstration that a nifJ homologue, when present, is not essential for nitrogen fixation in a diazotroph. The nifJ-like gene was sequenced a nd found to have considerable similarity to published nifJ gene sequen ces from other organisms, By primer extension, the initiation site for transcription was located, and a typical sigma(54) promoter sequence was identified.