Joint International Research Laboratory of Animal Health and Food Safety, College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, 210095, China.
College of Animal Science and Technology, Jinling Institute of Technology, Nanjing, 211169, China.
Vet Res. 2020 May 24;51(1):71. doi: 10.1186/s13567-020-00794-w.
The type VI secretion system (T6SS) is a multiprotein weapon that kills eukaryotic predators or prokaryotic competitors by delivering toxic effectors. Despite the importance of T6SS in bacterial environmental adaptation, it is still challenging to systematically identify T6SS effectors because of their high diversity and lack of conserved domains. In this report, we discovered a putative effector gene, U876-17730, in the whole genome of Aeromonas hydrophila NJ-35 based on the reported conservative domain DUF4123 (domain of unknown function), with two cognate immunity proteins encoded downstream. Phylogenetic tree analysis of amino acids indicates that AH17730 belongs to the Tle1 (type VI lipase effector) family, and therefore was named Tle1. The deletion of tle1 resulted in significantly decreased biofilm formation, antibacterial competition ability and virulence in zebrafish (Danio rerio) when compared to the wild-type strain. Only when the two immunity proteins coexist can bacteria protect themselves from the toxicity of Tle1. Further study shows that Tle1 is a kind of phospholipase that possesses a conserved lipase motif, Gly-X-Ser-X-Gly (X is for any amino acid). Tle1 is secreted by T6SS, and this secretion requires its interaction with an associated VgrG (valine-glycine repeat protein G). In conclusion, we identified a T6SS effector-immunity pair and verified its function, which lays the foundation for future research on the role of T6SS in the pathogenic mechanism of A. hydrophila.
VI 型分泌系统（T6SS）是一种多蛋白武器，通过输送毒性效应器来杀死真核捕食者或原核竞争者。尽管 T6SS 在细菌环境适应中具有重要意义，但由于其高度多样性和缺乏保守结构域，系统地鉴定 T6SS 效应器仍然具有挑战性。在本报告中，我们根据报道的保守结构域 DUF4123（未知功能结构域），在嗜水气单胞菌 NJ-35 的全基因组中发现了一个假定的效应子基因 U876-17730，该基因下游编码两个同源免疫蛋白。氨基酸的系统发育树分析表明，AH17730 属于 Tle1（VI 型脂肪酶效应子）家族，因此被命名为 Tle1。与野生型菌株相比，tle1 缺失导致生物膜形成、抗菌竞争能力和斑马鱼（Danio rerio）中的毒力显著降低。只有当两种免疫蛋白共存时，细菌才能免受 Tle1 的毒性。进一步的研究表明，Tle1 是一种磷脂酶，具有保守的脂肪酶基序 Gly-X-Ser-X-Gly（X 代表任何氨基酸）。Tle1 通过 T6SS 分泌，这种分泌需要其与相关的 VgrG（缬氨酸-甘氨酸重复蛋白 G）相互作用。总之，我们鉴定了一个 T6SS 效应器-免疫对，并验证了其功能，为进一步研究 T6SS 在嗜水气单胞菌致病机制中的作用奠定了基础。
