Viruses and their hosts are engaged in a constant arms race leading to the evolution of antiviral defence mechanisms. Recent studies have revealed that the immune arsenal of bacteria against bacteriophages is much more diverse than previously envisioned. These discoveries have led to seemingly contradictory observations: on one hand, individual microorganisms often encode multiple distinct defence systems, some of which are acquired by horizontal gene transfer, alluding to their fitness benefit. On the other hand, defence systems are frequently lost from prokaryotic genomes on short evolutionary time scales, suggesting that they impose a fitness cost. In this Perspective article, we present the 'pan-immune system' model in which we suggest that, although a single strain cannot carry all possible defence systems owing to their burden on fitness, it can employ horizontal gene transfer to access immune defence mechanisms encoded by closely related strains. Thus, the 'effective' immune system is not the one encoded by the genome of a single microorganism but rather by its pan-genome, comprising the sum of all immune systems available for a microorganism to horizontally acquire and use.

中文翻译：

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细菌的全免疫系统：作为社区资源的抗病毒防御。

病毒及其宿主参与不断的军备竞赛，从而导致了抗病毒防御机制的发展。最近的研究表明，细菌对噬菌体的免疫能力比以前设想的要多样化得多。这些发现导致了看似矛盾的观察结果：一方面，单个微生物经常编码多个不同的防御系统，其中一些是通过水平基因转移获得的，这暗示了它们的适用性。另一方面，防御系统经常在短的进化时间尺度上从原核基因组中丢失，这表明它们强加了适应成本。在这篇“观点”文章中，我们提出了“泛免疫系统”模型，在该模型中，我们建议，尽管单个菌株由于其适应性负担而无法携带所有可能的防御系统，但它可以利用水平基因转移来访问由密切相关的菌株编码的免疫防御机制。因此，“有效的”免疫系统不是由单个微生物的基因组编码的，而是由其泛基因组编码的，包括整个微生物可水平获取和使用的所有免疫系统的总和。