A prophage-expressed type IV pilus component provides anti-phage defense.

Phage genomes integrated within bacterial genomes, known as prophages, frequently encode proteins that provide defense against further phage infection. These proteins often function by altering the cell surface and preventing phages from attaching to their host receptor. Here, we describe prophage-encoded proteins that resemble FimU, a component of the Pseudomonas aeruginosa type 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 located. The phage FimU proteins and the phage tail proteins that likely interact with FimU are highly diverse, suggesting that evolution in this system is driven by phage versus phage competition. These phage FimU proteins represent an example of anti-phage defense mediated by the replacement of a bacterial cell surface component with a phage-encoded protein.