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Infect. Immun. doi:10.1128/IAI.00888-06
Copyright (c) 2006, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Role of RpoS in fine-tuning the synthesis of Vi capsular polysaccharide in Salmonella enterica serotype Typhi

The Biodesign Institute, Center for Infectious Diseases and Vaccinology. Arizona State University. Tempe, Arizona 85287. Department of Biology, Washington University, St. Louis, Missouri 63130

^* To whom correspondence should be addressed. Email: rcurtiss{at}asu.edu.

	Abstract

Regulation of the synthesis of Vi polysaccharide, a major virulence determinant in Salmonella enterica serotype Typhi (S. Typhi), is under the control of two regulatory systems, ompR-envZ and rscB-rscC, which respond to changes in osmolarity. Some S. Typhi strains exhibit over-expression of Vi polysaccharide, which masks clinical detection of LPS O-antigen. This variation in Vi polysaccharide and O-antigen display (VW variation) has been observed since the initial studies in S. Typhi. In this study, we report that the rpoS plays a role in this increased expression in Vi polysaccharide. We constructed a variety of S. Typhi isogenic mutants that differed in their expression of RpoS and examined the role of the rpoS product in synthesis of Vi polysaccharide under different osmolarities. Vi polysaccharide synthesis was also examined in S. Typhi mutants in which the native promoter of the rpoS was replaced by an araCP_BAD cassette, so that the expression of rpoS was arabinose-dependent. The RpoS^- strains showed an increased synthesis of Vi polysaccharide, which in low and medium osmolarities masked O-antigen detection. In contrast, RpoS⁺ strains showed lower synthesis of Vi polysaccharide and an increased detection of O-antigen was observed. During exponential growth, when rpoS is unstable or present at low levels, S. Typhi RpoS⁺ strains over-express the Vi polysaccharide at a level comparable to RpoS^- strains. Our results show that RpoS is another regulator of Vi polysaccharide synthesis and contributes to VW variation in S. Typhi, which has implications for development of recombinant attenuated Salmonella vaccines in humans.

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