Functional Metagenomic Selection Reveals Potent Cas9 Inhibitors in Human Oral and Fecal Metagenomes. human gut metagenome

CRISPR-Cas systems protect bacteria and archaea from phages and other mobile genetic elements, which use small anti-CRISPR (Acr) inhibitory proteins to overcome CRISPR-Cas immunity. Because they are difficult to identify, the natural diversity and impact of Acrs on microbial ecosystems is underappreciated. To overcome this discovery bottleneck, we developed a high-throughput functional selection that isolates Acrs based on their ability to inhibit CRISPR-Cas function. Using this selection, we discovered ten DNA fragments from human oral and fecal metagenomes that inhibit Streptococcus pyogenes Cas9.