CitAB Two-Component System-Regulated Citrate Utilization Contributes to <i>Vibrio cholerae</i> Competitiveness with the Gut Microbiota

Abstract

Citrate is a ubiquitous compound and can be utilized by many bacterial species, including enteric pathogens, as a carbon and energy source. Genes involved in citrate utilization have been extensively studied in some enteric bacteria, such as <i>Klebsiella pneumoniae</i>; however, their role in pathogenesis is still not clear. In this study, we investigated citrate utilization and regulation in <i>Vibrio cholerae</i>, the causative agent of cholera. The putative anaerobic citrate fermentation genes in <i>V. cholerae</i>, consisting of <i>citCDEFXG</i>, <i>citS-oadGAB</i>, and the two-component system (TCS) genes <i>citAB</i>, are highly homologous to those in <i>K. pneumoniae</i> Deletion analysis shows that these <i>cit</i> genes are essential for <i>V. cholerae</i> growth when citrate is the sole carbon source. The expression of <i>citC</i> and <i>citS</i> operons was dependent on citrate and CitAB, whose transcription was autorepressed and regulated by another TCS regulator, ArcA. In addition, citrate fermentation was under the control of catabolite repression. Mouse colonization experiments showed that <i>V. cholerae</i> can utilize citrate <i>in vivo</i> using the citrate fermentation pathway and that <i>V. cholerae</i> likely needs to compete with other members of the gut microbiota to access citrate in the gut.