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

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Abstract
In this study, we show thatSalmonellaproduces an O-antigen capsule coregulated with the fimbria- and cellulose-associated extracellular matrix. Structural analysis of purifiedSalmonellaextracellular polysaccharides yielded predominantly a repeating oligosaccharide unit similar to that ofSalmonella entericaserovar Enteritidis lipopolysaccharide O antigen with some modifications. Putative carbohydrate transport and regulatory operons important for capsule assembly and translocation, designatedyihU-yshAandyihVW, were identified by screening a random transposon library with immune serum generated to the capsule. The absence of capsule was confirmed by generating various isogenicΔyihmutants, whereyihQandyihOwere shown to be important in capsule assembly and translocation. Luciferase-based expression studies showed that AgfD regulates theyihoperons 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 theyihgenes 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.