Phase Variation and Expression of Capsular Polysaccharide in Vibrio vulnificus

Vibrio vulnificus is a natural bacterial inhabitant of bays and estuaries along the entire U. S. coastline. It causes devastating disease in humans and continues to be the leading cause of mortalities related to seafood consumption. Disease is primarily associated with eating raw oysters or with exposure of wounds to seawater. Aggressive attempts to increase public awareness have not been successful in reducing the number of cases, and increased dependence on foreign seafood markets and aquaculture may exacerbate the problem. The underlying disease mechanisms are still elusive; however, several laboratories have demonstrated that most, if not all, virulent strains produce a polysaccharide capsule. Interestingly, when grown under laboratory conditions, about 1 in every 1000 encapsulated cells spontaneously becomes capsule deficient and is no longer able to cause disease. This process is called phase variation and is a common theme for a number of bacterial species. The process is reversible, and deficient strains can recover capsular polysaccharide (CPS) expression. Phase variation may be driven by selective pressure from environmental factors such as starvation or stress. The genetic basis for phase variation in V. vulnificus is unknown. The investigators= previous work described factors that regulate CPS expression and identified a genetic locus for V. vulnificus CPS. Phase variation correlated with rearrangements at this locus. The proposed research will investigate the genetic basis for phase variation, and its influence on survival in the oyster. These studies should elucidate important disease determinants, increase understanding of the relationship of V. vulnificus to oysters, and perhaps provide future technologies with applications to seafood and aquaculture industries.