Department of Microbiology and Molecular Genetics, Harvard Medical School, Boston, MA 02115, USA.
Proc Natl Acad Sci U S A. 2010 Dec 7;107(49):21128-33. doi: 10.1073/pnas.1014998107. Epub 2010 Nov 17.
Vibrio cholerae is a human pathogen that causes the life-threatening diarrheal disease cholera. A type VI secretion system (T6SS) was recently shown to be required for full virulence in the O37 serogroup strain V52, which causes only sporadic human disease, but T6SS is not expressed in seventh pandemic O1 El Tor strains under standard laboratory conditions. In this study, we show that in the O1 El Tor strain C6706, T6SS is repressed by both quorum sensing and the uncharacterized protein VC0070 (TsrA). Disruption of TsrA and the quorum sensing regulator LuxO induces expression and secretion of the T6SS substrate Hcp, and this is dependent on the downstream regulator HapR, which directly binds to the promoter region of the T6SS genes hcp1 and hcp2 to induce expression. The activated T6SS in C6706 is functional and can translocate the effector protein VgrG-1 into macrophage cells, and T6SS activation leads to fecal diarrhea and intestinal inflammation in infant rabbits. Using an infant mouse infection model, we show that deletion of tsrA results in a 9.3-fold increase in intestinal colonization compared with wild type. TsrA functions as a global regulator to activate expression of hemagglutinin protease and repress cholera toxin and toxin coregulated pilus. Our findings provide significant insight into the molecular mechanism of T6SS and ToxT regulon gene regulation by quorum sensing and TsrA.
霍乱弧菌是一种人类病原体，可引起致命的腹泻病霍乱。最近的研究表明，一种类型 VI 分泌系统（T6SS）对于 O37 血清群菌株 V52 的完全毒力是必需的，该菌株仅导致散发性人类疾病，但在标准实验室条件下，第七次大流行 O1 型 El Tor 菌株不表达 T6SS。在这项研究中，我们表明在 O1 型 El Tor 菌株 C6706 中，T6SS 受到群体感应和未被描述的蛋白 VC0070（TsrA）的抑制。TsrA 和群体感应调节剂 LuxO 的缺失诱导 T6SS 底物 Hcp 的表达和分泌，这依赖于下游调节剂 HapR，其直接结合到 T6SS 基因 hcp1 和 hcp2 的启动子区域以诱导表达。在 C6706 中激活的 T6SS 是功能性的，可以将效应蛋白 VgrG-1 易位到巨噬细胞中，并且 T6SS 的激活导致幼兔粪便腹泻和肠道炎症。使用幼鼠感染模型，我们表明与野生型相比，tsrA 的缺失导致肠道定植增加了 9.3 倍。TsrA 作为一种全局调节剂，激活了血凝素蛋白酶的表达，并抑制了霍乱毒素和毒素调节菌毛。我们的发现为 T6SS 和 ToxT 调控子基因调节的分子机制提供了重要的见解，该调节由群体感应和 TsrA 介导。
