The bacterial immune system: identifying evolved defense adaptations.

A four-part framework reveals which bacterial defense mechanisms are true evolved adaptations, clarifying the expanding 'bacterial immune system' with 100+ new mechanisms annually.

• Why it matters: Understanding whether defense mechanisms are genuine evolutionary adaptations is crucial for accurately interpreting bacterial immunity and guiding microbiology research, yet no standardized criteria exist.
• What they did: The authors review evolutionary biology debates and develop a four-part framework to assess if bacterial defense mechanisms are evolved adaptations, providing a tool for future studies.
• The result: This framework enables researchers to distinguish true adaptations from incidental defenses, advancing clarity in microbiology and informing the study of bacterial immune strategies.