Identification of an anti-CRISPR protein that inhibits the CRISPR-Cas type I-B system inClostridioides difficile

Abstract

AbstractCRISPR-Cas systems provide their prokaryotic hosts with adaptive immunity against mobile genetic elements. Many bacteriophages encode anti-CRISPR (Acr) proteins that inhibit host defense. The identification of Acr proteins is challenging due to their small size and high sequence diversity, and only a limited number has been characterized to date. In this study, we report the discovery of a novel Acr protein, AcrIB2, encoded by the φCD38-2Clostridioides difficilephage that efficiently inhibits interference by the type I-B CRISPR-Cas system of the host and likely acts as a DNA mimic. MostC. difficilestrains contain twocasoperons, one encoding a full set of interference and adaptation proteins and another encoding interference proteins only. Unexpectedly, we show that only the partial operon is required for interference and is subject to inhibition by AcrIB2.