CRISPR provides bacteria with
CRISPR-Cas systems confer heritable sequence-specific defense fundamentally distinct from innate restriction-modification. Following initial infection, adaptation complex Cas1-Cas2 captures viral or plasmid protospacer DNA and integrates new spacer into leader-proximal end of CRISPR array. Upon reinfection, array transcribed and processed into crRNAs that guide Cas nucleases to complementary invader DNA or RNA for targeted cleavage. Spacer acquisition creates immunological memory improving resistance with repeated encounters, fulfilling criteria for Lamarckian inheritance. This adaptive character underpins repurposing for genome editing, while providing bacteria population-level immunity, spacer diversity, and protection against lytic phages preserving microbial ecosystems.
Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 5: CRISPR – Adaptive Immunity in Prokaryotes