CRISPR-Cas and restriction–modification systems are compatible and increase phage resistance

Bacteria have developed a set of barriers to protect themselves against invaders such as phage and plasmid nucleic acids. Different prokaryotic defence systems exist and at least two of them directly target the incoming DNA: restriction–modification (R-M) and CRISPR-Cas systems. On their own, they are imperfect barriers to invasion by foreign DNA. Here, we show that R-M and CRISPR-Cas systems are compatible and act together to increase the overall phage resistance of a bacterial cell by cleaving their respective target sites. Furthermore, we show that the specific methylation of phage DNA does not impair CRISPR-Cas acquisition or interference activities. Taken altogether, both mechanisms can be leveraged to decrease phage contaminations in processes relying on bacterial growth and/or fermentation