Calcium Enhances Bile Salt-Dependent Virulence Activation in Vibrio cholerae

Abstract

Vibrio cholerae is the causative bacteria of the diarrheal disease cholera, but it also persists in aquatic environments, where it displays an expression profile that is distinct from that during infection. Upon entry into the host, a tightly regulated circuit coordinates the induction of two major virulence factors: cholera toxin and a toxin-coregulated pilus (TCP). It has been shown that a set of bile salts, including taurocholate, serve as host signals to activate V. cholerae virulence through inducing the activity of the transmembrane virulence regulator TcpP. In this study, we investigated the role of calcium, an abundant mental ion in the gut, in the regulation of virulence. We show that whereas Ca 2ϩ alone does not affect virulence, Ca 2ϩ enhances bile salt-dependent virulence activation for V. cholerae. The induction of TCP by murine intestinal contents is counteracted when Ca 2ϩ is depleted by the high-affinity calcium chelator EGTA, suggesting that the calcium present in the gut is a relevant signal for V. cholerae virulence induction in vivo. We further show that Ca 2ϩ enhances virulence by promoting bile salt-induced TcpP-TcpP interaction. Moreover, fluorescence recovery after photobleaching (FRAP) analysis demonstrated that exposure to bile salts and Ca 2ϩ together decreases the recovery rate for fluorescently labeled TcpP, but not for another inner membrane protein (TatA). Together, these data support a model in which physiological levels of Ca 2ϩ may result in altered bile salt-induced TcpP protein movement and activity, ultimately leading to an increased expression of virulence.

Calcium Ions Modulate Amino Acid Sensing of the Chemoreceptor Mlp24 of Vibrio cholerae

“…Therefore, Ca 2ϩ is considered to be a cosignal for the primary signal mediated by Mlp24p, and it is possible that V. cholerae fine-tunes its chemotactic behavior in response to environmental calcium concentrations by modulating the ligand sensitivity of Mlp24, although the physiological role of the calcium dependency of the amino acid sensing is still unclear. It is known that calcium affects biofilm formation, cell adhesion, and other virulence activities in V. cholerae as well as other Vibrio species (16)(17)(18)(19)(20)(21).…”

Mechanisms of Bacterial Tolerance and Persistence in the Gastrointestinal and Respiratory Environments

“…Some studies have also been conducted with V. cholerae in relation to activation of the virulence factor associated with the metabolism of taurine and with bile salts, favoring colonization of the gastrointestinal tract (136)(137)(138)(139). Studies of the role of taurine (enzymes and transporters) associated with sulfate metabolism in this pathogen are scarce.…”

Calcium Signaling in Prokaryotes

“…No in vivo studies have been followed up. A more recent report in Vibrio cholera, showed that Ca 2+ greatly enhances the transmembrane virulence regulator (TcpP) activity by increasing protein-protein interaction in the presence of bile salts, leading to the activation of downstream virulence factors [10].…”

“…Although the role of Ca 2+ in prokaryotes is still unclear, there is increased evidence favoring a role for ([Ca 2+ ] i ) in signal transduction in bacteria. Indirect evidence shows that Ca 2+ affects several bacterial physiological processes including: chemotaxis, cell differentiation such as spore development and heterocyst formation, membrane transport (channels, primary and secondary transporters), virulence and host pathogen interactions [4,[6][7][8][9][10]. Similar to eukaryotes, bacteria maintain cytosolic free Ca 2+ within the nM range even in the presence of mM extracellular Ca 2+ [11][12][13][14][15].…”