Bacteriophage genomes encode both broad and specific counter-defense repertoires to overcome bacterial defense systems

Abstract

The evolutionary arms race between bacteria and bacteriophages drives rapid evolution of bacterial defense mechanisms with scattered distribution across genomes. We hypothesized that this variability in bacterial defense systems leads to equally variable counter-defense repertoires in phage genomes. Examining the variable regions in Pseudomonas model phages of the Pbunavirus genus revealed five anti-defense genes, including one inhibiting Druantia type III named DadIII-1, another targeting Thoeris type III named TadIII-1, one inhibiting Zorya type I named ZadI-1, and two related broad defense inhibitors named Bdi1 and Bdi2 targeting four defenses. A typical Pbunavirus encodes up to five known anti-defense genes, some inhibiting four unrelated defense systems with distinct nucleic-acid-targeting mechanisms. Structural homologs of broad-acting Bdi1 and Bdi2 are encoded across diverse phage taxa infecting multiple bacterial hosts. These findings show that phages face a variety of bacterial defenses, driving them to evolve both specific and general strategies to overcome these barriers.