State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, Shanghai 200237, China.
Department of Pathobiology and Veterinary Science, University of Connecticut, Storrs, CT 06269, USA.
Environ Microbiol. 2018 Feb;20(2):903-919. doi: 10.1111/1462-2920.14039. Epub 2018 Jan 19.
Type VI secretion systems (T6SS) are multiprotein secretion machines that can mediate killing of bacterial cells and thereby modify the composition of bacterial communities. The mechanisms that control the production of and secretion of these killing machines are incompletely understood, although quorum sensing (QS) and the PpkA kinase modulate T6SS activity in some organisms. Here we investigated control the T6S in the marine organism Vibrio alginolyticus EPGS, which encodes two T6SS systems (T6SS1 and T6SS2). We found that the organism principally relies on T6SS2 for interbacterial competition. We further carried out a phosphoproteomic screen to identify substrates of the T6SS2-linked PpkA2 kinase. Substrates of PpkA2 encoded within the T6SS2 cluster as well proteins that are apparently not linked to T6SS-related processes were identified. Similar to other organisms, PpkA2 autophosphorylation was critical for T6SS2 function. Notably, phosphorylation of a polypeptide encoded outside of the T6SS2 cluster, VtsR, was critical for T6SS2 expression and function because it augments the expression of luxR, a key regulator of QS that also promotes T6SS2 gene expression. Thus, PpkA2 controls a phosphorylation cascade that mediates a positive regulatory loop entwining T6SS and QS, thereby coordinating these pathways to enhance the competitive fitness of V. alginolyticus.
VI 型分泌系统（T6SS）是一种多蛋白分泌机器，可以介导细菌细胞的杀伤，从而改变细菌群落的组成。尽管群体感应（QS）和 PpkA 激酶在某些生物中调节这些杀伤机器的产生和分泌，但控制这些机器产生和分泌的机制尚不完全清楚。在这里，我们研究了海洋生物 Algolyticus EPGS 中的 T6S 控制，该生物编码了两种 T6SS 系统（T6SS1 和 T6SS2）。我们发现，该生物主要依靠 T6SS2 进行细菌间竞争。我们进一步进行了磷酸化蛋白质组筛选，以鉴定与 T6SS2 相关的 PpkA2 激酶的底物。鉴定了 T6SS2 簇内编码的 PpkA2 底物以及显然与 T6SS 相关过程无关的蛋白质。与其他生物一样，PpkA2 的自身磷酸化对于 T6SS2 的功能至关重要。值得注意的是，T6SS2 簇外编码的多肽 VtsR 的磷酸化对于 T6SS2 的表达和功能至关重要，因为它增强了 luxR 的表达，luxR 是 QS 的关键调节剂，也促进了 T6SS2 基因的表达。因此，PpkA2 控制着一种磷酸化级联反应，介导 T6SS 和 QS 的正调控环，从而协调这些途径以增强 Algolyticus 的竞争适应性。
