Role of RpoS in Fine-Tuning the Synthesis of Vi Capsular Polysaccharide inSalmonella entericaSerotype Typhi

Abstract

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 araCP BAD 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.

Regulation of Vi Capsular Polysaccharide Synthesis in Salmonella enterica Serotype Typhi

“…In one recent study, 36% of fresh human S. Typhi isolates were found to be rpoS mutants [53]. We confirmed that the rpoS allelic state is in fact responsible for these observations by constructing an rpoS deletion in ISP1820 [51]. In addition, we constructed an RpoS + derivative of Ty2.…”

“…However, rpoS might also contribute to the virulence of this serotype because RpoS − strains of S. Typhi are less cytotoxic than RpoS + strains, but RpoS − strains survive better inside resting THP-1 macrophages without apoptosis induction [50]. Recent studies in our laboratory indicate that there is a correlation between Vi polysaccharide over-expression and the allelic state of the rpoS gene [51].…”

“…The production of the H d flagellin, as well as Vi antigen, is modulated by the RcsB-RcsC regulatory system in response to changes in the osmolarity of the growth medium [25]. We have examined H d synthesis in strains with different rpoS genotypes grown in media with different osmolarities [51]. The synthesis of H d flagellar antigen in RpoS + strains was detected at all osmolarities tested.…”

Mechanisms of intrinsic resistance to antimicrobial peptides of Edwardsiella ictaluri and its influence on fish gut inflammation and virulence

“…The recombinant pEZ suicide vectors (Table S2) carrying the linked flanking regions to generate in-frame deletion of wibT, galF, gne and ugd genes were constructed as described previously (Santander et al, 2007(Santander et al, , 2011. The defined deletion mutations encompass a deletion including the ATG start codon, but do not include the TAG or TAA stop codon.…”

Typhi genes expressed during infection or involved in pathogenesis

“…The sigma factor RpoS is a global stationary phase regulator, controlling expression of many virulence associated systems, including Vi synthesis [56], and is required for virulence of Salmonella [57]. A mutation in rpoS renders Typhi less cytotoxic to THP-1 macrophages and although the mutant survives similarly to the wild-type strain [58], the mutant was less invasive on epithelial cells [59] (Table 1).…”