Control of bacterial virulence by AraC-like regulators that respond to chemical signals.

This review highlights the exciting new finding that small molecule inducers have been found for some members of the AraC family of transcriptional regulators (AFTRs) that control the expression of virulence genes of pathogenic bacteria. Although effector-mediated activation of AFTRs involved in the regulation of sugar and alkylbenzoate catabolism (e.g. AraC and XylS) is well understood, until recently little was known about effector-mediated regulation of virulence gene expression. This led to the belief that regulation of virulence by AFTRs does not involve the direct recognition of chemical environmental signals. More recently, however, a growing number of virulence-associated AFTRs have been found to directly sense environmental chemicals. Most interestingly, these environmental chemicals are abundant at the sites where the bacterial pathogen colonizes and damages its host. In this article we review recent developments in the field of environmental regulation mediated by virulence-associated AFTRs, with a focus on the sensing of environmental signals, the mechanism of gene target activation, and the effector-mediated modulation of regulator activities.