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Infection and Immunity, March 2007, p. 1382-1392, Vol. 75, No. 3
0019-9567/07/$08.00+0     doi:10.1128/IAI.00888-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Role of RpoS in Fine-Tuning the Synthesis of Vi Capsular Polysaccharide in Salmonella enterica Serotype Typhi{triangledown}

Javier Santander,1,2 Soo-Young Wanda,1,2 Cheryl A. Nickerson,1,2 and Roy Curtiss III1,2*

The Biodesign Institute, Center for Infectious Diseases and Vaccinology, Arizona State University, Tempe, Arizona 85287,1 Department of Biology, Washington University, St. Louis, Missouri 631302

Received 5 June 2006/ Returned for modification 31 July 2006/ Accepted 4 December 2006

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

* Corresponding author. Mailing address: The Biodesign Institute, Center for Infectious Diseases and Vaccinology, Arizona State University, PO Box 875401, 1001 S. McAllister Avenue, Tempe, AZ 85287-5401. Phone: (480) 727-0445. Fax: (480) 727-0466. E-mail: rcurtiss{at}asu.edu.

{triangledown} Published ahead of print on 18 December 2006.

Editor: F. C. Fang

Infection and Immunity, March 2007, p. 1382-1392, Vol. 75, No. 3
0019-9567/07/$08.00+0     doi:10.1128/IAI.00888-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



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