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Infect. Immun. doi:10.1128/IAI.01289-07
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Further characterization of Vibrio vulnificus rugose variants and identification of a capsular and rugose exopolysaccharide gene cluster

Department of Biological Sciences, Socolofsky Microscopy Center, Department of Pathobiological Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, Louisiana

^* To whom correspondence should be addressed. Email: gpettis{at}lsu.edu.

	Abstract

Capsular polysaccharide (CPS) is a major virulence factor in Vibrio vulnificus and encapsulated strains show an opaque, smooth (OpS) colony morphology while non-encapsulated strains are translucent and smooth (TrS). Previously we showed that OpS and TrS parental strains can yield a third colony type, rugose (R), and that the resulting strains, OpR and TrR, respectively, formed copious biofilms. Here we show that while OpR and TrR strains both produce three-dimensional biofilm structures that are indicative of rugose extracellular polysaccharide (rEPS) production, OpR strains also retain expression of CPS, and are virulent in an iron-supplemented mouse model while TrR strains lack CPS and are avirulent. Assays for chlorine resistance further distinguished OpR and TrR isolates as exposure to 3 µg/ml NaOCl eradicated both OpS and OpR strains, while TrS and TrR strains both survived, but at rates which were significantly different from one another. Taken together, these results further emphasize the importance of CPS for virulence of V. vulnificus and establish a correlation between CPS expression and chlorine sensitivity in this organism. Using reverse-transcriptase PCR, we also identified a nine-gene cluster associated with both CPS and rEPS expression in V. vulnificus, designated the wcr (capsular and rugose polysaccharide) locus, with expression occurring primarily in R variants. These latter results set the stage for characterization of functional determinants which individually or collectively contribute to expression of multiple extracellular polysaccharide forms in this pathogen.

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