Dark aerobic growth conditions induce the synthesis of a high midpoint potential cytochrome c(8) in the photosynthetic bacterium Rubrivivax gelatinosus

In several strains of the photosynthetic bacterium Rubrivivax gelatinosus, the synthesis of a high midpoint potential cytochrome is enhanced 4-6-fold in dark aerobically grown cells compared with anaerobic photosynthetic grow th. This observation explains the conflicting reports in the literature con cerning the cytochrome c content for this species. This cytochrome was isol ated and characterized in detail from Rubrivivax gelatinosus strain IL144. The redox midpoint potential of this cytochrome is +300 mV at pH 7. Its mol ecular mass, 9470 kDa, and its amino acid sequence, deduced from gene seque ncing, support its placement in the cytochrome cs family. The ratio of this cytochrome to reaction center lies between 0.8 and 1 for cells of Rvi. gel atinosus grown under dark aerobic conditions. Analysis of light-induced abs orption changes shows that this high-potential cytochrome cs can act in viv o as efficient electron donor to the photooxidized high-potential heme of t he Rvi. gelatinosus reaction center.