Delivery of an Rhs-family nuclease effector reveals direct penetration of the gram-positive cell envelope by a type VI secretion system in Acidovorax citrulli  

作　　者：Tong-Tong Pei Yumin Kan Zeng-Hang Wang Ming-Xuan Tang Hao Li Shuangquan Yan Yang Cui Hao-Yu Zheng Han Luo Xiaoye Liang Tao Dong 

机构地区：[1]State Key Laboratory of Microbial Metabolism,Joint International Research Laboratory of Metabolic&Developmental Sciences,School of Life Sciences and Biotechnology,Shanghai Jiao Tong University,Shanghai,China [2]Department of Immunology and Microbiology,School of Life Sciences,Southern University of Science and Technology,Guangdong,China

出　　处：《mLife》2022年第1期66-78,共13页微生物（英文）

基　　金：funding from the National Key R&D Program of China(2020YFA0907200);National Natural Science Foundation of China(31770082,32030001).

摘　　要：The type VI secretion system(T6SS)is a double-tubular nanomachine widely found in gram-negative bacteria.Its spear-like Hcp tube is capable of penetrating a neighboring cell for cytosol-to-cytosol protein delivery.However,gram-positive bacteria have been considered impenetrable to such T6SS action.Here we report that the T6SS of a plant pathogen,Acidovorax citrulli(AC),could deliver an Rhsfamily nuclease effector RhsB to kill not only gram-negative but also gram-positive bacteria.Using bioinformatic,biochemical,and genetic assays,we systematically identified T6SS-secreted effectors and determined that RhsB is a crucial antibacterial effector.RhsB contains an N-terminal PAAR domain,a middle Rhs domain,and an unknown C-terminal domain.RhsB is subject to self-cleavage at both its N-and C-terminal domains and its secretion requires the upstream-encoded chaperone EagT2 and VgrG3.The toxic Cterminus of RhsB exhibits DNase activities and such toxicity is neutralized by either of the two downstream immunity proteins,RimB1 and RimB2.Deletion of rhsB significantly impairs the ability of killing Bacillus subtilis while ectopic expression of immunity proteins RimB1 or RimB2 confers protection.We demonstrate that the AC T6SS not only can effectively outcompete Escherichia coli and B.subtilis in planta but also is highly potent in killing other bacterial and fungal species.Collectively,these findings highlight the greatly expanded capabilities of T6SS in modulating microbiome compositions in complex environments.

关 键 词：cell envelope cell wall interspecies interaction protein secretion 

分 类 号：Q78[生物学—分子生物学]