Discovery of multiple anti-CRISPRs highlights anti-defense gene clustering in mobile genetic elements
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Abstract
<jats:title>Abstract</jats:title> <jats:p> Many prokaryotes employ CRISPR–Cas systems to combat invading mobile genetic elements (MGEs). In response, some MGEs have developed strategies to bypass immunity, including anti-CRISPR (Acr) proteins; yet the diversity, distribution and spectrum of activity of this immune evasion strategy remain largely unknown. Here, we report the discovery of new Acrs by assaying candidate genes adjacent to a conserved Acr-associated (Aca) gene, <jats:italic>aca5</jats:italic> , against a panel of six type I systems: I–F ( <jats:italic>Pseudomonas</jats:italic> , <jats:italic>Pectobacterium</jats:italic> , and <jats:italic>Serratia</jats:italic> ), I–E ( <jats:italic>Pseudomonas</jats:italic> and <jats:italic>Serratia</jats:italic> ), and I–C ( <jats:italic>Pseudomonas</jats:italic> ). We uncover 11 type I–F and/or I–E anti-CRISPR genes encoded on chromosomal and extrachromosomal MGEs within <jats:italic>Enterobacteriaceae</jats:italic> and <jats:italic>Pseudomonas</jats:italic> , and an additional Aca ( <jats:italic>aca9</jats:italic> ). The <jats:italic>acr</jats:italic> genes not only associate with other <jats:italic>acr</jats:italic> genes, but also with genes encoding inhibitors of distinct bacterial defense systems. Thus, our findings highlight the potential exploitation of <jats:italic>acr</jats:italic> loci neighborhoods for the identification of previously undescribed anti-defense systems. </jats:p>