Virulent Salmonella typhimurium has two periplasmic Cu, Zn-superoxide dismutases

Periplasmic Cu, Zn-cofactored superoxide dismutase (SodC) protects Gram-neg ative bacteria from exogenous oxidative damage. The,virulent Salmonella typ himurium strain ATCC 14028s has been found to contain two discrete periplas mic Cu, Zn-SOD enzymes that are only 57% identical at the amino acid level. SodCI is carried by a cryptic bacteriophage, and SodCII is closely related to the Cu, Zn-superoxide dismutase of Escherichia coli, All Salmonella ser otypes appear to carry the sodCII locus, but the phage-associated sodCI gen e is found only in certain strains belonging to the most highly pathogenic serotypes, Expression of either sodC locus appears to be enhanced during st ationary phase, but only sodCII is regulated by the alternative sigma facto r sigma(s) (RpoS), Mutants lacking both sodC genes are less lethal for mice than mutants possessing either sodC locus alone, indicating that both Cu Z n-SOD enzymes contribute to Salmonella pathogenicity. The evolutionary acqu isition of an additional sodC gene has contributed to the enhanced virulenc e of selected Salmonella strains.