Recurring and emerging themes in prokaryotic innate immunity

A resurgence of interest in the pathways that bacteria use to protect against their viruses (i.e. phages) has led to the discovery of dozens of new antiphage defenses. Given the sheer abundance and diversity of phages — the ever-evolving targets of immunity — it is not surprising that these newly described defenses are also remarkably diverse. However, as their mechanisms slowly come into focus, some common strategies and themes are also beginning to emerge. This review highlights recurring and emerging themes in the mechanisms of innate immunity in bacteria and archaea, with an emphasis on recently described systems that have undergone more thorough mechanistic characterization.