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.Indole is a relatively recent addition to the list of signaling molecules used by bacteria and is produced as a by-product of the breakdown of tryptophan by the enzyme tryptophanase (TnaA) (18). Since the expression of the tnaA gene is controlled by catabolite repression, it is transcribed only during carbon limitation (57). As a result of this regulation, large quantities of indole are produced during the stationary phase of growth. Indole has long been known to act as a chemorepellent of Escherichia coli (52), but only more recently has indole also been shown to control the expression of a wide assortment of genes and phenotypes unrelated to chemotaxis in many different bacteria. For example, in E. coli indole controls the expression of genes involved in amino acid metabolism (54), plasmid maintenance (13), and quorum sensing (32), among other functions (14). Additionally, indole may function as an interspecies signal contributing to biofilm formation in an assortment of different bacteria known to carry a copy of the tryptophanase gene (36). In E. coli specifically, the indoledriven transcriptional response, which controls subsequent biofilm formation, is known to be controlled by the quorumsensing transcriptional regulator SdiA (32).It was previously shown that control of biofilm formation by indole also extends to the etiological agent of the ...

The atlastin GTPase couples nucleotide hydrolysis to formation of a trans cross-over dimer to catalyze homotypic endoplasmic reticulum membrane fusion. Assays that separate tethering from fusion reveal that stable trans contact for tethering depends on GTP hydrolysis. In contrast, cross-over formation is required only for the fusion step.

Before ER tubule fusion, the atlastin GTPase undergoes a “prefusion” to “postfusion” conformational change that is mediated by an intramolecular salt bridge.