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Microbiology 154 (2008), 979-988; DOI  10.1099/mic.0.2007/011999-0
© 2008 Society for General Microbiology

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

Claire Lewis1, Henrieta Skovierova2, Gary Rowley3, Bronislava Rezuchova2, Dagmar Homerova2, Andrew Stevenson1, Aileen Sherry1, Jan Kormanec2 and Mark Roberts1

1 Institute of Comparative Medicine, Faculty of Veterinary Medicine, University of Glasgow, Bearsden Road, Glasgow G61 1QH, UK
2 Institute of Molecular Biology, Slovak Academy of Science, Dubravska cesta 21, 845 51 Bratislava, Slovak Republik
3 School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, UK

Correspondence
Mark Roberts
m.roberts{at}vet.gla.ac.uk

SmpA is a small outer-membrane lipoprotein that is a component of the essential YaeT outer-membrane 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, SDS 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.

Abbreviations: ECF, extracytoplasmic function; ESR, envelope stress response; i.p., intraperitoneal; OMP, outer-membrane protein; TSP, transcriptional start point; WT, wild-type

Supplementary figures showing a comparison of the smpA promoter regions in the genera of the Enterobacteriales and an amino acid sequence alignment of SmpA/OmlA homologues of representatives of the three phylogenetic classes of proteobacteria are available with the online version of this paper.






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