Acquisition of novel arrays via horizontal gene transfer rewires CRISPR-mediated defense in Pseudomonas aeruginosa.

Horizontal gene transfer of isolated CRISPR arrays enables pan-immunity in Pseudomonas aeruginosa, with 1,196 genomes showing active transfer of these arrays.

• Why it matters: Understanding how bacteria acquire and maintain adaptive immunity is crucial for insights into microbial evolution and resistance mechanisms, especially given the prevalence of isolated CRISPR arrays far from cas genes.
• What they did: The study characterized the type I-F CRISPR-Cas system in P. aeruginosa, revealing that isolated arrays like CRISPR3 are horizontally transferred and actively participate in adaptive immunity through hyperactive primed adaptation.
• The result: This transfer of isolated arrays allows bacteria to mobilize immunological memory across populations, facilitating CRISPR-mediated pan-immunity and maintaining transferable immune memory within the pangenome.