Indole acts as an Extracellular Cue Regulating Gene Expression in Vibrio cholerae

Indole has been proposed to act as an extracellular signal molecule influencing biofilm formation in a range of bacteria. For this study, the role of indole in Vibrio cholerae biofilm formation was examined. It was shown that indole activates genes involved in vibrio polysaccharide (VPS) production, which is essential for V. cholerae biofilm formation. In addition to activating these genes, it was determined using microarrays that indole influences the expression of many other genes, including those involved in motility, protozoan grazing resistance, iron utilization, and ion transport. A transposon mutagenesis screen revealed additional components of the indole-VPS regulatory circuitry. The indole signaling cascade includes the DksA protein along with known regulators of VPS production, VpsR and CdgA. A working model is presented in which global control of gene expression by indole is coordinated through 54 and associated transcriptional regulators. Bacterial cells synthesize myriad small organic molecules to signal and adapt to environmental, physiological, and population structure changes. These molecules include extracellular signals such as acyl homoserine lactones, butyrolactones, quinolones, a furanosyl borate diester, oligopeptides, 3-hydroxypalmitic acid methyl ester, and a hydroxyketone and intracellular signals including cyclic nucleotides and ppGpp (25; reviewed in reference 11). The phenotypic response to signaling compounds often involves traits that are beneficial under adverse conditions, such as biofilm formation, virulence, motility, bioluminescence, sporulation, competence, modification of carbon and energy utilization, and macromolecule biosynthesis.