Laboratory of Molecular Microbiology, Global Health Institute, School of Life Sciences, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, CH-1015, Switzerland.
Environ Microbiol. 2020 Oct;22(10):4485-4504. doi: 10.1111/1462-2920.15224. Epub 2020 Oct 2.
Vibrio cholerae isolates responsible for cholera pandemics represent only a small portion of the diverse strains belonging to this species. Indeed, most V. cholerae are encountered in aquatic environments. To better understand the emergence of pandemic lineages, it is crucial to discern what differentiates pandemic strains from their environmental relatives. Here, we studied the interaction of environmental V. cholerae with eukaryotic predators or competing bacteria and tested the contributions of the haemolysin and the type VI secretion system (T6SS) to those interactions. Both of these molecular weapons are constitutively active in environmental isolates but subject to tight regulation in the pandemic clade. We showed that several environmental isolates resist amoebal grazing and that this anti-grazing defense relies on the strains' T6SS and its actincross-linking domain (ACD)-containing tip protein. Strains lacking the ACD were unable to defend themselves against grazing amoebae but maintained high levels of T6SS-dependent interbacterial killing. We explored the latter phenotype through whole-genome sequencing of 14 isolates, which unveiled a wide array of novel T6SS effector and (orphan) immunity proteins. By combining these in silico predictions with experimental validations, we showed that highly similar but non-identical immunity proteins were insufficient to provide cross-immunity among those wild strains.
霍乱弧菌分离株是引发霍乱大流行的罪魁祸首，但它们只代表了该物种中多样化菌株的一小部分。事实上，大多数霍乱弧菌存在于水生环境中。为了更好地了解大流行谱系的出现，区分大流行菌株与其环境亲缘菌株的差异至关重要。在这里，我们研究了环境霍乱弧菌与真核捕食者或竞争细菌的相互作用，并测试了溶血素和 VI 型分泌系统（T6SS）对这些相互作用的贡献。这两种分子武器在环境分离株中都是组成性激活的，但在大流行分支中受到严格调节。我们表明，一些环境分离株能够抵抗阿米巴原虫的吞噬，这种抗吞噬防御依赖于菌株的 T6SS 及其含有肌动蛋白交联结构域（ACD）的尖端蛋白。缺乏 ACD 的菌株无法抵御吞噬性阿米巴虫的侵袭，但仍能保持高水平的 T6SS 依赖性细菌间杀伤。我们通过对 14 个分离株的全基因组测序来探索后一种表型，揭示了一系列新型 T6SS 效应子和（孤儿）免疫蛋白。通过将这些计算预测与实验验证相结合，我们表明，高度相似但不完全相同的免疫蛋白不足以在这些野生菌株之间提供交叉免疫。
