Oxygen exposure increases resistance of Desulfovibrio vulgaris Hildenborough to killing by hydrogen peroxide

Abstract

Inactivation of PerR by oxidative stress and a corresponding increase in expression of the perR regulon genes is part of the oxidative stress defense in a variety of anaerobic bacteria. Diluted anaerobic, nearly sulfide-free cultures of mutant and wild-type Desulfovibrio vulgaris (10(5)-10(6) colony-forming units/ml) were treated with 0 to 2,500μM H(2)O(2) for only 5min to prevent readjustment of gene expression. Survivors were then scored by plating. The wild type and perR mutant had 50% survival at 58 and 269μM H(2)O(2), respectively, indicating the latter to be 4.6-fold more resistant to killing by H(2)O(2) under these conditions. Significantly increased resistance of the wild type (38-fold; 50% killing at 2188μM H(2)O(2)) was observed if cells were pretreated with full air for 30min, conditions that did not affect cell viability. The resistance of the perR mutant increased less (4.6-fold; 50% killing at 1230μM H(2)O(2)), when similarly pretreated. Interestingly, no increased resistance of either was achieved by exposure with 10.6μM H(2)O(2) for 30min, the highest concentration that could be used without killing the cells. Hence, in environments with low D. vulgaris biomass only the presence of external O(2) effectively activates the perR regulon. As a result, mutant strains lacking one of the perR regulon genes ahpC, dvu0772, rbr1 or rbr2 displayed decreased resistance to H(2)O(2) stress only following pretreatment with air.