Rubrerythrin and rubredoxin oxidoreductase in Desulfovibrio vulgaris: a novel oxidative stress protection system

Evidence is presented for an alternative to the superoxide dismutase (SOD)- catalase oxidative stress defense system in Desulfovibrio vulgaris (strain Hildenborough). This alternative system consists of the nonheme iron protei ns, rubrerythrin (Rbr) and rubredoxin oxidoreductase (Rbo), the product of the rbo gene (also called desulfoferrodoxin), A Delta rbo strain of D. vulg aris was found to be more sensitive to internal superoxide exposure than wa s the wild type. Unlike Rbo, expression of plasmid-borne Kbr failed to rest ore the aerobic growth of a SOD-deficient strain of Escherichia call. Conve rsely, plasmid-borne expression of two different Rbrs from D. vulgaris incr eased the viability of a catalase-deficient strain of E. call that had been exposed to hydrogen peroxide whereas Rbo actually decreased the viability. A previously undescribed D. vulgaris gene was found to encode a protein ha ving 50% sequence identity to that off. coli Fe-SOD. This gene also encoded an extended N-terminal sequence with high homologies to export signal pept ides of periplasmic redox proteins. The SOD activity of D. vulgaris is not affected by the absence of Rbo and is concentrated in the periplasmic fract ion of cell extracts. These results are consistent with a superoxide reduct ase rather than SOD activity of Rbo and with a peroxidase activity of Rbr. A joint role for Rbo and Rbr as a novel cytoplasmic oxidative stress protec tion system in D. vulgaris and other anaerobic microorganisms is proposed.