VceR negatively regulates the vceCAB MDR efflux operon and positively regulates its own synthesis in Vibrio cholerae 569B

The vceCAB (vce) operon encodes the multidrug resistance pump VceCAB (VCE), which contributes to resistance of Vibrio cholerae to carbonyl cyanide m-chlorophenylhydrazine (CCCP), deoxycholate, and pentachlorophenol by several-fold. vceR, which encodes the TetR-type repressor VceR and is divergently transcribed from vce, has been characterized in Escherichia coh. Detailed characterization of vceR in V cholerae 569B confirmed the repressive effect of VceR on VCE function and indicated several novel features of VceR. Deletion of vceR increased resistance of strain 569B to CCCP and deoxycholate modestly, but did not affect resistance to pentachlorophenol. Transcriptional analysis revealed that vce expression was not only increased in strain 569B Delta vceR::Omega by 2-fold but continued to rise throughout the growth cycle. Using a veeR-lux transcriptional fusion plasmid, we examined whether vceR is autoregulated in strain 569B. Expression of vceR from the vceR-lux fusion was significantly lower in strain 569B Delta vceR::Omega than in strain 569B. In addition, exposure to CCCP reduced vceR expression from the vceR-lux fusion in strain 569B but not in strain 569B Delta vceR::Omega. Despite differences in the VceR binding site in strain 569B from the previously recognized 28 bp sequence in V. cholerae CVD101, purified recombinant VceR bound to the 24 bp sequence from strain 569B. We propose that VceR modulates vce expression by binding in vivo to the 24 bp sequence within the vce.R-vce intergenic region; unlike many TetR repressors that are negatively autoregulated, VceR positively regulates vceR expression in trans.