Effect of Fatty Acids and Cholesterol Present in Bile on Expression of Virulence Factors and Motility of Vibrio cholerae

Abstract

Bile induces pleiotropic responses that affect production of virulence factors, motility, and other phenotypes in the enteric pathogen Vibrio cholerae. Since bile is a heterogeneous mixture, crude bile was fractionated, and the components that mediate virulence gene repression and enhancement of motility were identified by nuclear magnetic resonance, gas chromatography (GC), and GC-mass spectrometry analyses. The unsaturated fatty acids detected in bile, arachidonic, linoleic, and oleic acids, drastically repressed expression of the ctxAB and tcpA genes, which encode cholera toxin and the major subunit of the toxin-coregulated pilus, respectively. The unsaturated fatty acid-dependent repression was due to silencing of ctxAB and tcpA expression by the histonelike nucleoid-structuring protein H-NS, even in the presence of the transcriptional activator ToxT. Unsaturated fatty acids also enhanced motility of V. cholerae due to increased expression of flrA, the first gene of a regulatory cascade that controls motility. H-NS had no role in the fatty acid-mediated enhancement of motility. It is likely that the ToxR/ToxT system that negatively regulates motility is rendered nonfunctional in the presence of unsaturated fatty acids, leading to an increase in motility. Motility and flrA expression were also increased in the presence of cholesterol, another component of bile, in an H-NS-and ToxR/ToxT-independent manner.Vibrio cholerae, a noninvasive enteric bacterium, is the causative agent of the diarrheal disease cholera. Cholera continues to cause devastating outbreaks, particularly in the developing world, resulting in more than 100,000 deaths every year, and the case fatality ratio may exceed 20% in affected populations (29). The pathogenicity of V. cholerae is largely due to the production of cholera toxin (CT) and a toxin-coregulated pilus (TCP), thought to be essential for colonization of the intestinal epithelium by the bacterium (13). Expression of CT, TCP, and several other virulence factors is coordinately controlled by the hierarchical expression of regulatory proteins comprising the ToxR regulon (14), in which the inner membrane DNA binding proteins ToxR and TcpP (7, 18) activate expression of ToxT, a transcriptional regulator that is required for the expression of ctxAB and tcpA as well as several other virulence genes (3). The ToxR regulon is strongly influenced by physicochemical parameters/factors such as temperature, osmolarity, pH, amino acids, and bile, which exert their effects at different levels of the regulatory cascade (16, 25).Bile, a heterogeneous mixture of conjugated and unconjugated bile acids, bile pigments, inorganic salts, cholesterol, phospholipids, and probably other unidentified components, is secreted into the lumen of the duodenum from the gall bladder through the bile duct and is inevitably encountered by all enteric bacteria in their human hosts (9). The role of bile in normal gastrointestinal physiology is to aid the emulsification of lipids and also to protect the host from bacteri...

Bile salt–induced intermolecular disulfide bond formation activates Vibrio cholerae virulence

“…Further studies are required to fully understand how V. cholerae integrates these host signals. Intriguingly, fatty acids present in bile negatively regulate virulence gene expression (9), indicative of fine-tuned negative feedback of virulence gene regulation, further illuminating the complexity of the host-pathogen interaction.…”

“…It has been reported that certain environmental conditions such as temperature, oxygen concentration, osmolarity, pH, and iron availability (4-6) influence expression of virulence genes in vitro. In addition, bicarbonate and fatty acids, which are abundant in host small intestines, modulate virulence gene expression through ToxT (7)(8)(9). Intriguingly, different in vitro conditions are required to activate virulence genes in different biotypes of V. cholerae.…”

Regulation of Bacterial Virulence by Csr (Rsm) Systems

“…cholerae primarily inhabits aquatic environments and causes the human disease known as cholera (290). Virulent serogroups of V. cholerae form robust biofilms and express the virulence factors cholera toxin (CT) and the toxin-coregulated pilus (TCP) (290,291). The maturation and dispersal of V. cholerae biofilms, as well as the production of CT and TCP, are controlled by multiple independent quorum-sensing systems, whose effects converge on a single regulatory circuit (Fig.…”

How can Naturally Occurring Fatty Acids Neutralize Listeria ?

“…These findings suggest that FFAs act by blocking the activity of PrfA, possibly by generating an inhibitory signaling event via the membrane, or by direct binding to the PrfA protein itself [4]. Interestingly, unsaturated long-chain FFAs present in bile are known to inhibit the expression of two primary virulence genes in Vibrio cholera, encoding the cholera toxin and toxin-coregulated pilus [11]. The transcription factor ToxT, belonging to the AraC family, directly activates expression of cholera toxin and toxin-coregulated pilus, but the presence of unsaturated long-chain FFAs inhibits ToxT-dependent activation.…”