Small outer-membrane lipoprotein, SmpA, is regulated by σE and has a role in cell envelope integrity and virulence of Salmonella enterica serovar Typhimurium

SmpA is a small outer-membrane lipoprotein that is a component of the essential YaeT outermembrane protein assembly complex. In Salmonella enterica serovar Typhimurium (S. Typhimurium), expression of the smpA gene was shown to be directed by two promoters, smpAp1 and smpAp2. The more distal promoter, smpAp1, is dependent upon the extracytoplasmic stress response sigma factor sigma(E). An smpA null mutant was constructed in S. Typhimurium SL1344 and was shown to be more sensitive than its wild-type parent to growth at high temperature and in the presence of sodium cholate, SIDS plus EDTA, and the hydrophobic antibiotic rifampicin. The lack of SmpA in S. Typhimurium elicits a sigma(E)-dependent stress response, These findings are indicative of altered outer-membrane integrity in the smpA mutant, probably due to a defect in outer-membrane protein biogenesis. SmpA was not important for entry or survival within murine macrophages; however, the S. Typhimurium smpA mutant was attenuated in mice by both the oral and parenteral routes of infection, and SmpA appeared to be most important for the growth of S. Typhimurium at systemic sites.