Bacteria require a number of systems, including the type VI secretion system (T6SS), for interbacterial competition and pathogenesis. The T6SS is a large nanomachine that can deliver toxins directly across membranes of proximal target cells. Since major reassembly of T6SS is necessary after each secretion event, accurate timing and localization of T6SS assembly can lower the cost of protein translocation. Although critically important, mechanisms underlying spatiotemporal regulation of T6SS assembly remain poorly understood. Here, we used super-resolution live-cell imaging to show that while Acinetobacter and Burkholderia thailandensis can assemble T6SS at any site, a significant subset of T6SS assemblies localizes precisely to the site of contact between neighboring bacteria. We identified a class of diverse, previously uncharacterized, periplasmic proteins required for this dynamic localization of T6SS to cell–cell contact (TslA). This precise localization is also dependent on the outer membrane porin OmpA. Our analysis links transmembrane communication to accurate timing and localization of T6SS assembly as well as uncovers a pathway allowing bacterial cells to respond to cell–cell contact during interbacterial competition.

中文翻译：

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VI型分泌系统组装响应细胞-细胞接触的亚细胞定位

细菌需要许多系统来进行细菌间竞争和发病机制，包括 VI 型分泌系统 (T6SS)。T6SS 是一种大型纳米机器，可以将毒素直接输送到近端靶细胞的膜上。由于每次分泌事件后 T6SS 的主要重新组装是必要的，因此 T6SS 组装的准确时间和定位可以降低蛋白质易位的成本。尽管至关重要，但对 T6SS 组装的时空调控机制仍然知之甚少。在这里，我们使用超分辨率活细胞成像显示，不动杆菌和伯克霍尔德氏菌可以在任何位置组装 T6SS，T6SS 组装的重要子集精确定位到相邻细菌之间的接触位置。我们确定了一类多样的、以前未表征的周质蛋白，这些蛋白是 T6SS 动态定位到细胞 - 细胞接触 (TslA) 所需的。这种精确定位也依赖于外膜孔蛋白 OmpA。我们的分析将跨膜通讯与 T6SS 组装的准确时间和定位联系起来，并揭示了一条允许细菌细胞在细菌间竞争期间对细胞间接触作出反应的途径。