is a natural inhabitant of aquatic ecosystems. Some strains of can colonize the human host and cause cholera, a profuse watery diarrhea. The major pathogenicity factors and virulence regulators of are either encoded in mobile genetic elements acquired in the environment (e.g. pathogenicity islands or lysogenic phages) or in the core genome. Several lines of evidence indicate that the emergence of numerous virulence traits of occurred in its natural environment due to biotic and abiotic pressures. Here, we discuss the connection between the human host and the potential ecological role of these virulent traits. Unraveling these connections will help us understand the emergence of this organism and other facultative bacterial pathogens.