Project Summary Vibrio vulnificus is a natural inhabitant of coastal waters, including the US Gulf. The bacterium causes severe life threatening infections after consumption of contaminated seafood (especially raw oysters) and from wounds contaminated by seawater. Among food-borne pathogens, V. vulnificus is most notable for its high rates of hospitalization and death and its negative economic impact. Indeed, V. vulnificus accounts for 72% of deaths from Vibrio illnesses despite causing only 13% of infections. Although infections are rare, the number of serious infections has been increasing globaly due to climate change that has caused a rise in the number of days amenable to growth of V. vulnificus in coastal waters and the geographical area amenable to the pathogen. Attempts by various agency to warn and protect citezens by implementation of new policies or issuing warnings have met with resistance for it effect on the shellfish harvesting industry and the tourist economy. Thus, the study of V. vulnificus pathogenesis has become both a food safety and public policy priority. A significant virulence factor of V. vulnificus is the large Multifunctional-Autoprocessing RTX toxin (MARTXVv). This toxin is comprised of long repeat regions that are associated with cellular necrosis, but this activity is not sufficient for virulence. Rather, virulence is associated with “effector domains” that are translocated across host plasma membrane by repeat regions, and then released to the cell cytosol by inositol hexakisphophate induced autoprocessing. Bioinformatics studies reveal that different clinical isolates of V. vulnificus express distinct forms of the toxin, with five different variants assembled from eight different MARTX effector domains. To date, the mechanism of action of five of these domains has been determined. In this project, we will investigate the mechanism of action of the remaining effector domains found in clinical isolates. Further, we will study the relative toxicity of different variants of MARTXVv toxin in pathogenesis by the food- borne route of infection.