The genus Vibrio contains several of the most important pathogens known. One member of this group, Vibrio vulnificus, is an estuarine bacterium which is the causative agent of both food-borne disease and wound infection. Vibrio vulnificus is ubiquitous in estuarine waters and occurs in molluscan shellfish in high numbers. However, the incidence of disease is relatively low and it has been suggested that not all strains of V. vulnificus are equally virulent. We have previously shown that there is a dimorphism present in the vcg (virulence correlated gene) locus of V. vulnificus, with the vcgC (clinical) and vcgE (environmental) alleles strongly correlating with either clinical or environmental isolation source. In this study, an examination of eight V. vulnificus genes for which there is sufficient data showed that such a C/E dimorphism is present in each gene examined, including housekeeping genes. Additionally, we found that the C and E genotypes of V. vulnificus respond in markedly different ways to environmental conditions. These findings lead us to hypothesize that the C and E genotypes also represent different ecotypes, possibly in the process of diverging into separate species.