Rubredoxin:: Oxygen oxidoreductase enhances survival of Desulfovibrio vulgatis Hildenborough under microaerophilic conditions

Genes for superoxide reductase (Sor), rubredoxin (Rub), and rubredoxin:oxygen oxidoreductase (Roo) are located in close proximity in the chromosome of Desulfovibrio vulgaris Hildenborough. Protein blots confirmed the absence of Roo from roo mutant and sor-rub-roo (srr) mutant cells and its presence in sor mutant and wild-type cells grown under anaerobic conditions. Oxygen reduction rates of the roo and srr mutants were 20 to 40% lower than those of the wild type and the sor mutant, indicating that Roo functions as an O-2 reductase in vivo. Survival of single cells incubated for 5 days on agar plates under microaerophilic conditions (1% air) was 85% for the sor, 4% for the roo, and 0.7% for the srr mutant relative to that of the wild type (100%). The similar survival rates of sor mutant and wild-type cells suggest that O-2 reduction by Roo prevents the formation of reactive oxygen species (ROS) under these conditions; i.e., the ROS-reducing enzyme Sor is only needed for survival when Roo is missing. In contrast, the sor mutant was inactivated much more rapidly than the roo mutant when liquid cultures were incubated in 100% air, indicating that O-2 reduction by Roo and other terminal oxidases did not prevent ROS formation under these conditions. Competition of Sor and Roo for limited reduced Rub was suggested by the observation that the roo mutant survived better than the wild type under fully aerobic conditions. The roo mutant was more strongly inhibited than the wild type by the nitric oxide (NO)-generating compound S-nitrosoglutathione, indicating that Roo may also serve as an NO reductase in vivo.