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Original Research | Open Access

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

Tong-Tong Pei1, Yumin Kan1, Zeng-Hang Wang1, Ming-Xuan Tang1, Hao Li1, Shuangquan Yan1, Yang Cui1, Hao-Yu Zheng1, Han Luo1, Xiaoye Liang1, Tao Dong1,2 ( )
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
Department of Immunology and Microbiology, School of Life Sciences, Southern University of Science and Technology, Guangdong, China

Edited by Wei Qian, Institute of Microbiology, Chinese Academy of Sciences, China

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Abstract

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 Rhs-family 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 C-terminus 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.

Keywords

cell wallcell envelopeinterspecies interactionprotein secretion

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mLife
Volume 1 Issue 1,
March 2022
Pages 66-78
DOI: 10.1002/mlf2.12007
Cite this article:
Pei T-T, Kan Y, Wang Z-H, et al. 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. mLife, 2022, 1(1): 66-78. https://doi.org/10.1002/mlf2.12007

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Received: 06 October 2021
Accepted: 16 December 2021
Published: 24 March 2022
© 2022 The Authors. mLife published by John Wiley & Sons Australia, Ltd. on behalf of Institute of Microbiology, Chinese Academy of Sciences.

This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
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