Molecular control of bacterial immunity.

Phage infection places strong selective pressure on bacteria to mount a rapid immune response to ensure survival. Although recent studies have uncovered a wide diversity of bacterial immune systems, how these systems function under the tight time constraints of phage infection remains poorly understood. Here we summarize structural, biochemical and genetic insights into bacterial immunity, focusing on steps that link infection sensing to activation and effector function. We highlight how conformational change, protein assembly and spatial organization shape immune activation, and how phages employ counter-defense strategies that disrupt these processes.