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Salmonella Produces an O-Antigen Capsule Regulated by AgfD and Important for Environmental Persistence

Department of Biochemistry and Microbiology, University of Victoria, Victoria, V8W 3P6 British Columbia, Canada,¹ Department of Microbiology and Infectious Diseases, University of Calgary, Calgary, T2N 4N1 Alberta, Canada,² Complex Carbohydrate Research Center, Athens, Georgia 30602-4712³

Received 7 June 2006/ Accepted 25 July 2006

In this study, we show that Salmonella produces an O-antigen capsule coregulated with the fimbria- and cellulose-associated extracellular matrix. Structural analysis of purified Salmonella extracellular polysaccharides yielded predominantly a repeating oligosaccharide unit similar to that of Salmonella enterica serovar Enteritidis lipopolysaccharide O antigen with some modifications. Putative carbohydrate transport and regulatory operons important for capsule assembly and translocation, designated yihU-yshA and yihVW, were identified by screening a random transposon library with immune serum generated to the capsule. The absence of capsule was confirmed by generating various isogenic yih mutants, where yihQ and yihO were shown to be important in capsule assembly and translocation. Luciferase-based expression studies showed that AgfD regulates the yih operons in coordination with extracellular matrix genes coding for thin aggregative fimbriae and cellulose. Although the capsule did not appear to be important for multicellular behavior, we demonstrate that it was important for survival during desiccation stress. Since the yih genes are conserved in salmonellae and the O-antigen capsule was important for environmental persistence, the formation of this surface structure may represent a conserved survival strategy.

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