Physiological Role Analyzed by Gene Disruption of Membrane-Bound Cytochrome c Working as an Electron Donor to the Photochemical Reaction Center Complex in the Purple Bacterium, Rhodovulum sulfidophilum

Abstract

A marine purple photosynthetic bacterium, Rhodovulum sulfidophilum, synthesizes a membrane-bound cyatochrome c, in addition to the water-soluble cytochrome c₂, as a possible electron donor to the photochemical reaction center. The gene coding for this cytochrome c was cloned and analyzed. The deduced molecular weight was 50,528. Its C-terminal heme-containing region showed the highest sequence identity to the water-soluble cytochromes c₂. Phylogenetic analyses suggested that this membrane-bound cytochrome c has evolved from cytochromes c₂. Mutants lacking this cytochrome or cytochrome c₂ showed the same growth rate as the wild type. However, a double mutant lacking both cytochromes c showed no growth under photosynthetic conditions. It was concluded that either the membrane-bound cytochrome c or the water-soluble cytochrome c₂ work as a physiological electron carrier in the photosynthetic electron transfer pathway of R. sulfidophilum.