Expression and Degradation of SEp22, a Pathogenicity-Related Protein of Salmonella Dps, in Salmonella enterica serovar Enteritidis Isolated from the Poultry Farms in Japan

Abstract

We isolated and characterized a pathogenicity-related protein in Salmonella enterica serovar Enteritidis (SE) from poultry farms, and designated it as SEp22, which has recently been identified with Salmonella Dps, a DNA-binding protein (12, 13, Amano et al., manuscript in preparation). Expression of SEp22 was shown to be transcriptionally regulated, because another SE strain without virulence was found to possess a full-length non-mutated gene of sep22, but had little expression of SEp22 mRNA and much lower levels of SEp22 protein compared to the virulent standard strain SE Cl#15-1. Besides, expression of SEp22 was connected with bacterial growth, showing reduced expression in the logarithmic phase but increased expression from the late logarithmic to stationary phases. These changes were slightly later than those in σ 3 8 levels as well as SEp22 mRNA, suggesting that expression of SEp22 is under transcriptional control through RNA polymerase activity by σ 3 8 . In addition, high levels of SEp22 in the stationary phase were rapidly reduced upon incubation of the bacteria in fresh medium. This reduction was dependent on bacterial concentration in the culture, temperature, and time of incubation, suggesting proteolytic degradation of SEp22 in growing bacteria.