Integration of prophages into CRISPR loci remodels viral immunity in Streptococcus pyogenes

Abstract

SummaryCRISPR loci are composed of short DNA repeats separated by sequences that match the genomes of phages and plasmids, known as spacers. Spacers are transcribed and processed to generate RNA guides used by CRISPR-associated nucleases to recognize and destroy the complementary nucleic acids of invaders. To counteract this defense, phages can produce small proteins that inhibit these nucleases. Here we demonstrate that the ΦAP1.1 temperate phage utilizes an alternate approach to antagonize the type II-A CRISPR response in Streptococcus pyogenes. Immediately after infection this phage expresses a canonical anti-CRISPR, AcrIIA23 that prevents Cas9 function, allowing ΦAP1.1 to integrate into the direct repeats of the CRISPR locus and neutralizing immunity. However, acrIIA23 is not transcribed during lysogeny and phage integration/excision cycles can result in the deletion and/or transfer of spacers, enabling a complex modulation of the type II-A CRISPR immune response.