Interactive control of Rhodobacter capsulatus redox-balancing systems during phototrophic metabolism

In nonsulfur purple bacteria, redox homeostasis is achieved by the coordina te control of various oxidation-reduction balancing mechanisms during photo trophic anaerobic respiration. In this study, the ability of Rhodobacter ca psulatus to maintain a balanced intracellular oxidation-reduction potential was considered; in addition,, interrelationships between the control of kn own redox-balancing systems, the Calvin-Benson-Bassham, dinitrogenase and d imethyl sulfoxide reductase systems, were probed in strains grown under bot h photoheterotrophic and photoautotrophic growth conditions. By using cbb(I ) (cbb form I operon)-, cbb(II)-, nifH-, and dorC-reporter gene fusions, it was demonstrated that each redox-balancing system responds to specific met abolic circumstances under phototrophic growth conditions. In specific muta nt strains of R. capsulatus, expression of both the Calvin-Benson-Bassham a nd dinitrogenase systems was influenced by dimethyl sulfoxide respiration. Under photoheterotrophic growth conditions, coordinate control of redox-bal ancing systems was further manifested in ribulose 1,5-bisphosphate carboxyl ase/oxygenase and phosphoribulokinase deletion strains. These findings demo nstrated the, existence of interactive control mechanisms that govern the d iverse means by which R. capsulatus maintains redox poise during photoheter otrophic and photoautotrophic growth.