The evolutionary arms race between bacteria and phages led to the emergence of bacterial immune systems whose diversity and dynamics remain poorly understood. Here we use comparative genomics to describe a widespread genetic element, defined by the presence of the Gamma-Mobile-Trio (GMT) proteins, that serves as a reservoir of offensive and defensive tools. We demonstrate, using Vibrio parahaemolyticus as a model, that GMT-containing genomic islands are active mobile elements. Furthermore, we show that GMT islands’ cargoes contain various anti-phage defence systems, antibacterial type VI secretion system (T6SS) effectors and antibiotic-resistance genes. We reveal four anti-phage defence systems encoded within GMT islands and further characterize one system, GAPS1, showing it is triggered by a phage capsid protein to induce cell dormancy. Our findings underscore the need to broaden the concept of ‘defence islands’ to include defensive and offensive tools, as both share the same mobile elements for dissemination.

细菌和噬菌体之间的进化军备竞赛导致了细菌免疫系统的出现，其多样性和动力学仍然知之甚少。在这里，我们使用比较基因组学来描述一种广泛的遗传元件，其定义是 Gamma-Mobile-Trio （GMT） 蛋白的存在，它是进攻和防御工具的储存库。我们使用副溶血性弧菌作为模型证明，含有 GMT 的基因组岛是活跃的移动元件。此外，我们表明 GMT 岛的货物包含各种抗噬菌体防御系统、抗菌 VI 型分泌系统 （T6SS） 效应器和抗生素耐药基因。我们揭示了在 GMT 岛中编码的四种抗噬菌体防御系统，并进一步表征了一个系统 GAPS1，表明它由噬菌体衣壳蛋白触发以诱导细胞休眠。我们的研究结果强调，需要扩大“防御岛”的概念，以包括防御和进攻工具，因为两者都具有相同的传播移动元素。