Taylor Dawn L, Ante Vanessa M, Bina X Renee, Howard Mondraya F, Bina James E
University of Pittsburgh School of Medicine, Department of Microbiology and Molecular Genetics, Pittsburgh, Pennsylvania, United States of America.
PLoS One. 2015 Feb 19;10(2):e0117890. doi: 10.1371/journal.pone.0117890. eCollection 2015.
Vibrio cholerae encodes six resistance-nodulation-division (RND) efflux systems which function in antimicrobial resistance, virulence factor production, and intestinal colonization. Among the six RND efflux systems, VexAB exhibited broad substrate specificity and played a predominant role in intrinsic antimicrobial resistance. The VexAB system was encoded in an apparent three gene operon that included vexR; which encodes an uncharacterized TetR family regulator. In this work we examined the role of vexR in vexRAB expression. We found that VexR bound to the vexRAB promoter and vexR deletion resulted in decreased vexRAB expression and increased susceptibility to VexAB antimicrobial substrates. Substrate-dependent induction of vexRAB was dependent on vexR and episomal vexR expression provided a growth advantage in the presence of the VexAB substrate deoxycholate. The expression of vexRAB increased, in a vexR-dependent manner, in response to the loss of RND efflux activity. This suggested that VexAB may function to export intracellular metabolites. Support for this hypothesis was provided by data showing that vexRAB was upregulated in several metabolic mutants including tryptophan biosynthetic mutants that were predicted to accumulate indole. In addition, vexRAB was found to be upregulated in response to exogenous indole and to contribute to indole resistance. The collective results indicate that vexR is required for vexRAB expression in response to VexAB substrates and that the VexAB RND efflux system modulates the intracellular levels of metabolites that could otherwise accumulate to toxic levels.
霍乱弧菌编码六种耐药-结瘤-分裂（RND）外排系统，这些系统在抗菌耐药性、毒力因子产生和肠道定植中发挥作用。在这六种RND外排系统中，VexAB表现出广泛的底物特异性，并在固有抗菌耐药性中起主要作用。VexAB系统由一个明显的三基因操纵子编码，其中包括vexR；vexR编码一种未表征的TetR家族调节因子。在这项工作中，我们研究了vexR在vexRAB表达中的作用。我们发现VexR与vexRAB启动子结合，vexR缺失导致vexRAB表达降低，并增加了对VexAB抗菌底物的敏感性。vexRAB的底物依赖性诱导依赖于vexR，并且附加体vexR表达在存在VexAB底物脱氧胆酸盐的情况下提供了生长优势。响应RND外排活性的丧失，vexRAB的表达以vexR依赖的方式增加。这表明VexAB可能起到输出细胞内代谢物的作用。显示vexRAB在包括预计会积累吲哚的色氨酸生物合成突变体在内的几种代谢突变体中上调的数据为这一假设提供了支持。此外，发现vexRAB对外源吲哚有反应而上调，并有助于吲哚抗性。总体结果表明，vexR是响应VexAB底物时vexRAB表达所必需的，并且VexAB RND外排系统调节细胞内代谢物水平，否则这些代谢物可能积累到有毒水平。
