Department of Molecular Biology, Umeå University, S-901 87 Umeå, Sweden.
Environ Microbiol. 2009 Dec;11(12):3018-28. doi: 10.1111/j.1462-2920.2009.02005.x. Epub 2009 Jul 14.
Type VI protein secretion systems (T6SS) are essential for virulence of several Gram-negative bacteria. In this study, we identified a T6SS in Vibrio anguillarum, a marine bacterium that causes a hemorrhagic septicemia in fish. A partial operon vtsA-H (vibrio type six secretion) was sequenced and shown to encode eight proteins. VtsE-H are signature proteins found in other T6SSs, while VtsA-D are not associated with T6SS studied so far. In-frame deletions were made in each gene. Secretion of a haemolysin-co-regulated-like protein (Hcp), a protein secreted by all studied T6SSs, was decreased in VtsE-H. Unexpectedly, VtsA, VtsC and VtsD activated while VtsB and VtsE-H repressed hcp expression. The T6SS proteins also regulated expression of two extracellular proteases, EmpA and PrtV, but inversely to Hcp expression. This regulation was indirect as T6S positively regulated expression of the stress-response regulator RpoS and the quorum-sensing regulator VanT, which positively regulate protease expression. Moreover, VtsA-H proteins were not needed for virulence but did play a role in various stress responses. Thus, these data characterize a new role for T6S in the ecology of bacteria and we hypothesize this role to be a signal sensing mechanism that modulates the expression of regulators of the general stress response.
VI 型蛋白分泌系统（T6SS）对于几种革兰氏阴性菌的毒力至关重要。在这项研究中，我们在海洋细菌鳗弧菌中鉴定出了一种 T6SS，这种细菌会导致鱼类出血性败血病。我们对一个部分操纵子 vtsA-H（弧菌六型分泌系统）进行了测序，并表明其编码了 8 种蛋白质。VtsE-H 是其他 T6SS 中发现的特征蛋白，而 VtsA-D 与迄今为止研究的 T6SS 无关。我们在每个基因中都进行了框内缺失。一种溶血素共同调节样蛋白（Hcp）的分泌减少了，Hcp 是所有研究过的 T6SS 分泌的一种蛋白。出乎意料的是，VtsA、VtsC 和 VtsD 被激活，而 VtsB 和 VtsE-H 则抑制了 hcp 的表达。T6SS 蛋白还调节了两种细胞外蛋白酶 EmpA 和 PrtV 的表达，但与 Hcp 的表达相反。这种调节是间接的，因为 T6S 正向调节应激反应调节因子 RpoS 和群体感应调节因子 VanT 的表达，而 RpoS 和 VanT 正向调节蛋白酶的表达。此外，VtsA-H 蛋白对于毒力不是必需的，但确实在各种应激反应中发挥作用。因此，这些数据描述了 T6S 在细菌生态学中的一个新作用，我们假设这个作用是一种信号感应机制，调节一般应激反应调节因子的表达。
