We isolated and characterized a pathogenicity-related protein in Salmonella Enteritidis (SE) from poultry farms, and designated it as SEp22, which was identified later as Salmonella Dps, a DNA-binding protein from starved cells. Expression of SEp22 was regulated by bacterial growth in Luria-Bertani (LB) medium, showing reduced expression in the logarithmic phase but increased expression from the late logarithmic to stationary phases, which was linked to the expression of σS both in protein as well as mRNA levels. In addition, induction of SEp22 required nutritional factors in LB or casamino acids during overnight incubation in M9 minimal medium, or even through short-term exposure to H2O2 for 5-15 min. Induction of SEp22 was also remarkable after sudden addition of H2O2 and exposure of the bacteria to the drying protocol. The roles of SEp22 in the pathogenicity of Salmonella in mice, the survival of Salmonella exposed to H2O2, or that under dry-stress were proved not only by the difference among Salmonella clones from environmental isolates with different levels of SEp22 expression, but also by sep22-gene-depleted mutants that originated from SECl#15-1, a wild type virulent strain with high levels of SEp22. These results suggest that SEp22 is a key molecule that is responsible for pathogenesis as well as environmental stress-resistance. In this review, the diverse roles of SEp22/Dps in Salmonella are also described, suggesting the importance of this protein in the bacterial stress responses in infection and survival, as well as in the regulation of bacterial growth through aerobic metabolism. Recent progress in SEp22/Dps research at the molecular levels is also discussed.
2011 by The Pharmaceutical Society of Japan