Cholerae Biofilm Formation Research Articles

Indole Acts as an Extracellular Cue Regulating Gene Expression inVibrio 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 sigma(54) and associated transcriptional regulators.

Temporal Quorum-Sensing Induction Regulates Vibrio cholerae Biofilm Architecture

Vibrio cholerae, the pathogen that causes cholera, also survives in aqueous reservoirs, probably in the form of biofilms. Quorum sensing negatively regulates V. cholerae biofilm formation through HapR, whose expression is induced at a high cell density. In this study, we show that the concentration of the quorum-sensing signal molecule CAI-1 is higher in biofilms than in planktonic cultures. By measuring hapR expression and activity, we found that the induction of quorum sensing in biofilm-associated cells occurs earlier. We further demonstrate that the timing of hapR expression is crucial for biofilm thickness, biofilm detachment rates, and intestinal colonization efficiency. These results suggest that V. cholerae is able to regulate its biofilm architecture by temporal induction of quorum-sensing systems.

NspS, a Predicted Polyamine Sensor, Mediates Activation of Vibrio cholerae Biofilm Formation by Norspermidine

Vibrio cholerae is both an environmental bacterium and a human intestinal pathogen. The attachment of bacteria to surfaces in biofilms is thought to be an important feature of the survival of this bacterium both in the environment and within the human host. Biofilm formation occurs when cell-surface and cell-cell contacts are formed to make a three-dimensional structure characterized by pillars of bacteria interspersed with water channels. In monosaccharide-rich conditions, the formation of the V. cholerae biofilm requires synthesis of the VPS exopolysaccharide. MbaA (locus VC0703), an integral membrane protein containing a periplasmic domain as well as cytoplasmic GGDEF and EAL domains, has been previously identified as a repressor of V. cholerae biofilm formation. In this work, we have studied the role of the protein NspS (locus VC0704) in V. cholerae biofilm development. This protein is homologous to PotD, a periplasmic spermidine-binding protein of Escherichia coli. We show that the deletion of nspS decreases biofilm development and transcription of exopolysaccharide synthesis genes. Furthermore, we demonstrate that the polyamine norspermidine activates V. cholerae biofilm formation in an MbaA- and NspS-dependent manner. Based on these results, we propose that the interaction of the norspermidine-NspS complex with the periplasmic portion of MbaA diminishes the ability of MbaA to inhibit V. cholerae biofilm formation. Norspermidine has been detected in bacteria, archaea, plants, and bivalves. We suggest that norspermidine serves as an intercellular signaling molecule that mediates the attachment of V. cholerae to the biotic surfaces presented by one or more of these organisms.

Cyclic Diguanylate Regulates Vibrio cholerae Virulence Gene Expression

The cyclic dinucleotide second messenger cyclic diguanylate (c-diGMP) has been implicated in regulation of cell surface properties in several bacterial species, including Vibrio cholerae. Expression of genes required for V. cholerae biofilm formation is activated by an increased intracellular c-diGMP concentration. The response regulator VieA, which contains a domain responsible for degradation of c-diGMP, is required to maintain a low concentration of c-diGMP and repress biofilm formation. The VieSAB three-component signal transduction system was, however, originally identified as a regulator of ctxAB, the genes encoding cholera toxin (CT). Here we show that the c-diGMP phosphodiesterase activity of VieA is required to enhance CT production. This regulation occurred at the transcriptional level, and ectopically altering the c-diGMP concentration by expression of diguanylate cyclase or phosphodiesterase enzymes also affected ctxAB transcription. The c-diGMP phosphodiesterase activity of VieA was also required for maximal transcription toxT but did not influence the activity of ToxR or expression of TcpP. Finally, a single amino acid substitution in VieA that increases the intracellular c-diGMP concentration led to attenuation in the infant mouse model of cholera. Since virulence genes including toxT and ctxA are repressed by a high concentration of c-diGMP, while biofilm genes are activated, we suggest that c-diGMP signaling is important for the transition of V. cholerae from the environment to the host.