Vibrio cholerae biofilms: stuck between a rock and a hard place.

Vibrio cholerae is a diarrheal pathogen and a natural inhabitant of freshand saltwater environments. Seasonal outbreaks in areas of endemicity that can develop into worldwide pandemics are linked to the persistence of V. cholerae in aquatic ecosystems, providing a reservoir for the initiation of new cholera epidemics via human ingestion of contaminated food or water (7). Biofilm formation is dependent on the production of an exopolysaccharide (EPS) (13, 17), and the previous finding by the Klose laboratory that a flagellum-dependent pathway induces EPS expression (14) has led to their surprising discovery reported in this issue: the sodium-driven flagellar motor is intimately involved in EPS expression, biofilm formation, and the virulence of V. cholerae (6). The EPS signaling cascade appears to operate through a flagellar motor-based mechanosensor mechanism (5, 6) adapted by bacteria to induce appropriate behaviors on solid surfaces and perhaps additional behaviors in the diverse microenvironments encountered during their life cycle.