Prophages express a type IV pilus component to provide anti-phage defence

Phage genomes integrated within bacterial genomes, known as prophages, frequently encode proteins that provide defence against further phage infection. These proteins often function at the cell surface and prevent phages from attaching to their host receptor. Here, we describe the discovery of prophage-encoded proteins that resemble FimU, a component of thePseudomonas aeruginosatype IV pilus. These phage FimU proteins are incorporated into the pilus without altering its function, yet they mediate robust protection against infection by phages that bind to the tip of the pilus, where FimU is likely located. The phage FimU proteins and the phage tail proteins that interact with FimU are highly diverse, suggesting that evolution in this system is driven by phage versus phage competition. To our knowledge, this is the first example of anti-phage defence mediated by replacement of a bacterial cell surface component with a phage-encoded protein.