%0 Journal Article %A Willison, John C. %A Vignais, Paulette M. %T The Use of Metronidazole to Isolate Nif− Mutants of Rhodopseudomonas capsulata, and the Identification of a Mutant with Altered Regulatory Properties of Nitrogenase %D 1982 %J Microbiology, %V 128 %N 12 %P 3001-3010 %@ 1465-2080 %R https://doi.org/10.1099/00221287-128-12-3001 %I Microbiology Society, %X Metronidazole (2-methyl-5-nitroimidazole-l-ethanol) was used to select nitrogen fixation (Nif−) mutants of Rhodopseudomonas capsulata, either by enrichment with metronidazole, or by direct selection on agar medium containing the drug. By the latter method, approximately 50% of the isolates obtained were Nif−. Several Nif− mutants showed the phenotype expected for mutants defective in electron transport to nitrogenase: their nitrogenase activity (determined as rate of acetylene reduction) relative to that of the wild-type strain was higher when assayed in toluene-treated cells in the presence of dithionite, than when assayed in resting cell suspensions with dl-malate as source of electrons. Glutamate-grown cells of one such mutant (RC5) resembled N-starved cells of the wild-type, and differed from glutamate-grown cells of the wild type in that nitrogenase activity in toluene-treated cells was unaffected by the addition of Mn2+ and the rate of H2 production by resting cell suspensions was significantly higher than the rate of acetylene reduction. These observations implied that glutamate-grown cells of the mutant contained predominantly nitrogenase A, the form of nitrogenase which is independent of the Mn2+-dependent membrane-bound activating factor, suggesting that the mutant may be affected in the interconversion of nitrogenase between the regulatory forms A and R. %U https://www.microbiologyresearch.org/content/journal/micro/10.1099/00221287-128-12-3001