PDF(Pubmed)
Abstract：
The Type VI secretion system (T6SS) is a multicomponent apparatus, present in many Gram-negative bacteria, which can inhibit bacterial prey in various ecological niches. Pseudomonas aeruginosa assembles one of its three T6SS (H1-T6SS) to respond to attacks from adjacent competing bacteria. Surprisingly, repeated assemblies of the H1-T6SS, termed dueling, were described in a monoculture in the absence of an attacker strain; however, the underlying mechanism was unknown. Here, we explored the role of H2-T6SS of P. aeruginosa in triggering H1-T6SS assembly. We show that H2-T6SS inactivation in P. aeruginosa causes a significant reduction in H1-T6SS dueling and that H2-T6SS activity directly triggers retaliation by the H1-T6SS. Intraspecific competition experiments revealed that elimination of H2-T6SS in non-immune prey cells conferred protection from H1-T6SS. Moreover, we show that the H1-T6SS response is triggered independently of the characterized lipase effectors of the H2-T6SS, as well as those of Acinetobacter baylyi and Vibrio cholerae. Our results suggest that H1-T6SS response to H2-T6SS in P. aeruginosa can impact intraspecific competition, particularly when the H1-T6SS effector-immunity pairs differ between strains, and could determine the outcome of multistrain colonization.IMPORTANCEThe opportunistic pathogen Pseudomonas aeruginosa harbors three different Type VI secretion systems (H1, H2, and H3-T6SS), which can translocate toxins that can inhibit bacterial competitors or inflict damage to eukaryotic host cells. Unlike the unregulated T6SS assembly in other Gram-negative bacteria, the H1-T6SS in P. aeruginosa is precisely assembled as a response to various cell damaging attacks from neighboring bacterial cells. Surprisingly, it was observed that neighboring P. aeruginosa cells repeatedly assemble their H1-T6SS toward each other. Mechanisms triggering this \"dueling\" behavior between sister cells were unknown. In this report, we used a combination of microscopy, genetic and intraspecific competition experiments to show that H2-T6SS initiates H1-T6SS dueling. Our study highlights the interplay between different T6SS clusters in P. aeruginosa, which may influence the outcomes of multistrain competition in various ecological settings such as biofilm formation and colonization of cystic fibrosis lungs.
摘要：
VI型分泌系统（T6SS）是一种多组分器官，存在于许多革兰氏阴性细菌中，可以抑制各种生态位的细菌猎物。铜绿假单胞菌组装其三个T6SS中的一个(H1-T6SS)以响应来自邻近竞争细菌的攻击。令人惊讶的是,H1-T6SS的重复组装，称为决斗，在没有攻击者菌株的情况下，在单一文化中进行了描述；然而，潜在的机制是未知的。这里,我们探讨了铜绿假单胞菌H2-T6SS在触发H1-T6SS组装中的作用。我们表明，铜绿假单胞菌中的H2-T6SS失活导致H1-T6SS决斗显着减少，并且H2-T6SS活性直接触发H1-T6SS的报复。种内竞争实验表明，在非免疫猎物细胞中消除H2-T6SS可保护H1-T6SS。此外，我们表明，H1-T6SS反应的触发独立于H2-T6SS的表征脂肪酶效应子，以及鲍氏不动杆菌和霍乱弧菌。我们的结果表明，H1-T6SS响应H2-T6SS在铜绿假单胞菌可以影响种内竞争，特别是当H1-T6SS效应子免疫对在菌株之间不同时，并可以确定多菌株定植的结果。机会致病菌铜绿假单胞菌有三种不同的VI型分泌系统（H1、H2和H3-T6SS），可以转运毒素，这些毒素可以抑制细菌竞争者或对真核宿主细胞造成损害。与其他革兰氏阴性细菌中不受调节的T6SS组装不同，铜绿假单胞菌中的H1-T6SS作为对来自邻近细菌细胞的各种细胞损伤攻击的响应而被精确地组装。令人惊讶的是,观察到邻近的铜绿假单胞菌细胞重复地相互组装它们的H1-T6SS。引发姐妹细胞之间这种“决斗”行为的机制尚不清楚。在这份报告中,我们使用了显微镜的组合，遗传和种内竞争实验表明H2-T6SS启动H1-T6SS决斗。我们的研究强调了铜绿假单胞菌不同T6SS簇之间的相互作用，这可能会影响各种生态环境中的多菌株竞争结果，例如生物膜的形成和囊性纤维化肺的定植。
