Phages overcome bacterial immunity via diverse anti-defence proteins.

It was recently shown that bacteria employ, apart from CRISPR-Cas and restriction systems, a considerable diversity of phage resistance systems 1-4 , but it is largely unknown how phages cope with this multilayered bacterial immunity. Here, we analyzed groups of closely related Bacillus phages that showed differential sensitivity to bacterial defense systems, and discovered four distinct families of anti-defense proteins that inhibit the Gabija, Thoeris, and Hachiman systems. We show that these proteins Gad1, Gad2, Tad2, and Had1 efficiently cancel the defensive activity when co-expressed with the respective defense system or introduced into phage genomes. Homologs of these anti-defense proteins are found in hundreds of phages that infect taxonomically diverse bacterial species. We show that the anti-Gabija protein Gad1 blocks the ability of the Gabija defense complex to cleave phage-derived DNA. Our data further reveal an anti-Thoeris protein, denoted Tad2, which is a "sponge" that sequesters the immune signaling molecules produced by Thoeris TIR-domain proteins in response to phage. Our results demonstrate that phages encode an arsenal of anti-defense proteins that can disable a variety of bacterial defense mechanisms.