B-173. The Effects of Bile and Temperature on Virulence Factor Expression in Vibrio cholerae

M. Bellair, J. Withey;
Wayne State Univ., Detroit, MI.

Vibrio cholerae is a gram-negative, curved rod bacterium that is the causative agent of the diarrheal disease cholera. ToxT protein, a member of the AraC/XylS family of transcriptional factors, directly activates the virulence factors produced by the bacterium. V. cholerae expresses two major virulence factors, cholera toxin (CT) and toxin co-regulated pilus (TCP), as well as several other factors whose role in pathogenesis are not well understood. Several environmental signals, including bile and temperature, have been shown to affect the cascade of regulatory proteins involved in activating virulence factor expression. Bile is an alkaline fluid secreted by the gallbladder, and is discharged into the duodenum upon eating. Therefore, V. cholerae is likely to encounter bile in the small intestine in its early stages of infection. To assess the role of bile on ToxT-dependent gene expression, we assayed for the activity of various reporter gene constructs in the presence and/or absence of 0.4% bile at 30ºC. Bile was found to lower activity of all reporter gene constructs tested, indicating that ToxT-dependent transcriptional activity is affected by the presence of bile. Decrease in activity of all reporter constructs also illustrates that bile is not specific for any individual promoter, but rather affects all promoters that are activated by ToxT. An increase in temperature from 30ºC to 37ºC in the absence of bile showed an increase in activity of all reporter gene constructs, in contrast to published results showing a decrease in activity at 37ºC. However, activity decreases with addition of 0.4% bile at 37ºC, indicating that the effects of bile are not temperature-dependent.