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Many photosynthetic bacteria use inorganic sulfur compounds as electron donors for carbon dioxide fixation. A thiosulfate-induced cytochrome c has been purified from the photosynthetic alpha-proteobacterium Rhodovulum sulfidophilum. This cytochrome c(551) is a heterodimer of a diheme 30-kDa SoxA subunit and a monoheme 15-kDa SoxX subunit. The cytochrome c(551) structural genes are part of an 11-gene sox locus. Sequence analysis suggests that the ligands to the heme iron in SoxX are a methionine and a histidine, while both SoxA hemes are predicted to have unusual cysteine-plus-histidine coordination. A soxA mutant strain is unable to grow photoautotrophically on or oxidize either thiosulfate or sulfide. Cytochrome c(551) is thus essential for the metabolism of both these sulfur species. Periplasmic extracts of wild-type R. sulfidophilum exhibit thiosulfate:cytochrome c oxidoreductase activity. However, such activity can only be measured for a soxA mutant strain if the periplasmic extract is supplemented with purified cytochrome c(551). Gene clusters similar to the R. sulfidophilum sox locus can be found in the genome of a green sulfur bacterium and in phylogenetically diverse nonphotosynthetic autotrophs.

Original publication

DOI

10.1128/JB.183.20.6107-6118.2001

Type

Journal article

Journal

J Bacteriol

Publication Date

10/2001

Volume

183

Pages

6107 - 6118

Keywords

Alphaproteobacteria, Amino Acid Sequence, Bacterial Proteins, Cloning, Molecular, Cytochrome c Group, Enzyme Induction, Genes, Bacterial, Marine Biology, Molecular Sequence Data, Mutagenesis, Insertional, Oxidation-Reduction, Oxidoreductases, Periplasm, Photosynthesis, Sequence Analysis, DNA, Sequence Homology, Amino Acid, Sulfides, Thiosulfates, Water Microbiology