Complex I and its involvement in redox homeostasis and carbon and nitrogen metabolism in Rhodobacter capsulatus

A transposon mutant of Rhodobacter capsulatus, strain Mal7, that was incapable of photoautotrophic and chemoautotrophic growth and could not grow photoheterotrophically in the absence of an exogenous electron acceptor was isolated. The phenotype of strain Mal7 suggested that the mutation was in some gene(s) not previously shown to be involved in CO(2) fixation control. The site of transposition in strain Mal7 was identified and shown to be in the gene nuoF, which encodes one of the 14 subunits for NADH ubiquinone-oxidoreductase, or complex I. To confirm the role of complex I and nuoF for CO(2)-dependent growth, a site-directed nuoF mutant was constructed (strain SBC1) in wild-type strain SB1003. The complex I-deficient strains Mal7 and SBC1 exhibited identical phenotypes, and the pattern of CO(2) fixation control through the Calvin-Benson-Bassham pathway was the same for both strains. It addition, it was shown that electron transport through complex I led to differential control of the two major cbb operons of this organism. Complex I was further shown to be linked to the control of nitrogen metabolism during anaerobic photosynthetic growth of R. capsulatus.