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Infection and Immunity, January 2009, p. 501-507, Vol. 77, No. 1
0019-9567/09/$08.00+0     doi:10.1128/IAI.00850-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Role of RpoS in the Virulence of Citrobacter rodentium{triangledown}

Tao Dong,1 Brian K. Coombes,2 and Herb E. Schellhorn1*

Department of Biology, Life Sciences Building, Rm. 433, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4K1, Canada,1 Department of Biochemistry and Biomedical Sciences, Health Sciences Centre, 4H17, McMaster University, 1200 Main St. West, Hamilton, Ontario L8N 3Z5, Canada2

Received 9 July 2008/ Returned for modification 3 September 2008/ Accepted 22 October 2008

Citrobacter rodentium is a mouse enteropathogen that is closely related to Escherichia coli and causes severe colonic hyperplasia and bloody diarrhea. C. rodentium infection requires expression of genes of the locus of enterocyte effacement (LEE) pathogenicity island, which simulates infection by enteropathogenic E. coli and enterohemorrhagic E. coli in the human intestine, providing an effective model for studying enteropathogenesis. In this study we investigated the role of RpoS, the stationary phase sigma factor, in virulence in C. rodentium. Sequence analysis showed that the rpoS gene is highly conserved in C. rodentium and E. coli, exhibiting 92% identity. RpoS was critical for survival under heat shock conditions and during exposure to H2O2 and positively regulated the expression of catalase KatE (HPII). The development of the RDAR (red dry and rough) morphotype, an important virulence trait in E. coli, was also mediated by RpoS in C. rodentium. Unlike E. coli, C. rodentium grew well in the mouse colon, and the wild-type strain colonized significantly better than rpoS mutants. However, a mutation in rpoS conferred a competitive growth advantage over the wild type both in vitro in Luria-Bertani medium and in vivo in the mouse colon. Survival analysis showed that the virulence of an rpoS mutant was attenuated. The expression of genes on the LEE pathogenicity island, which are essential for colonization and virulence, was reduced in the rpoS mutant. In conclusion, RpoS is important for the stress response and is required for full virulence in C. rodentium.

* Corresponding author. Mailing address: Department of Biology, Life Sciences Building, Rm. 433, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4K1, Canada. Phone: (905) 525-9140, ext. 27316. Fax: (905) 522-6066. E-mail: schell{at}mcmaster.ca

{triangledown} Published ahead of print on 3 November 2008.

Editor: J. B. Bliska

Infection and Immunity, January 2009, p. 501-507, Vol. 77, No. 1
0019-9567/09/$08.00+0     doi:10.1128/IAI.00850-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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