Spontaneous Nif/sup -/ mutants of Rhodopseudomonas capsulata
摘要
Revertible, spontaneous Nif/sup -/ mutants of Rhodopseudomonas capsulata have been shown to accumulate in cultures growing photosynthetically with an amino acid as the nitrogen source such that H/sub 2/ is maximally produced. The majority of such strains carry mutations which are clustered in a short region of the chromosome, probably representing one or two genes. Because this cluster includes temperature-sensitive mutations, it is also likely that it identifies the structural gene of a polypeptide. The phenotypic characterization of these spontaneous mutants showed (1) an inability to grow with N/sub 2/ as the nitrogen source, (2) no measurable nitrogenase activity, (3) a reduction or absence of the three polypeptides of the MoFe and Fe proteins of the nitrogenase complex, (4) a faster growth rate on glutamate as the nitrogen source under saturating light, and (5) frequently a small increase in glutamine synthetase activity relative to that of the wild type when grown with glutamate as the nitrogen source. Alterations in other ammonium-assimilatory enzyme activities were not observed. Taken together, these properties suggest that the mutations have affected a regulatory protein necessary for nitrogen fixation. 28 references, 4 figures, 4 tables.