Surviving phage attack primes bacterial immunity to defeat counterdefenses.

Transcriptional repressors with ligand-responsive WYL domains control diverse bacterial defense systems, yet the natural cues driving derepression and the physiological rationale for dynamic regulation in native host-phage contexts remain unknown. Here, we show that restricted phage infection, where defense clears a primary attack, serves as a natural cue for WYL-mediated derepression in Vibrio cholerae . Although not required to block the initial infection, this response increases defense protein abundance, shifting host-phage stoichiometry and priming surviving bacteria to overwhelm phage-encoded counterdefenses in subsequent attacks. We also find that restricted infection co-induces an unlinked anti-plasmid defense via its own WYL repressor, showing that parallel WYL sensors coordinate a broader immune response without regulatory crosstalk. In contrast, productive phage infection triggers horizontal transfer of the defense-encoding mobile element, ensuring its persistence in the population. Together, our work reveals that infection fate dictates divergent outcomes for the expression and dissemination of bacterial immunity.