Role of sodium bioenergetics in Vibrio cholerae

The ability of the bacterium to use sodium in bioenergetic processes appear s to play a key role in both the environmental and pathogenic phases of Vib rio cholerae. Aquatic environments, including fresh, brackish, and coastal waters, are an important factor in the transmission of cholera and an autoc hthonous source. The organism is considered to be halophilic and has a stri ct requirement for Na+ for growth. Furthernore, expression of motility and virulence factors of V. cholerae is intimately linked to sodium bioenergeti cs and to each other. Several lines of evidence indicated that the activity of the flagellum of V cholerae might have an impact on virulence gene regu lation. As the V. cholerae flagellum is sodium-driven and the Na+-NQR enzym e is known to create a sodium motive force across the bacterial membrane, i t was recently suggested that the increased toxT expression observed in a n qr-negative strain is mediated by affecting flagella activity. It was sugge sted that the V. cholerae flagellum might respond to changes in membrane po tential and the resulting changes in flagellar rotation might serve as a si gnal for virulence gene expression. However, we recently demonstrated that although the flagellum of V cholerae is not required for the effects of ion ophores on virulence gene expression, changes in the sodium chemical potent ial are sensed and thus alternative mechanisms, perhaps involving the TcpP/ H proteins, for the detection of these conditions must exist. Analyzing the underlying mechanisms by which bacteria respond to changes in the environm ent, such as their ability to monitor the level of membrane potential, will probably reveal complex interplays between basic physiological processes a nd virulence factor expression in a variety of pathogenic species. (C) 2001 Published by Elsevier Science B.V.