Prophages block cell surface receptors to ensure survival of their viral progeny

In microbial communities, viruses compete for host cells to infect, and thus evolved diverse ways to inhibit their competitors. One mechanism is Superinfection exclusion (Sie), whereby a virus that has established an infection prevents a secondary infection. We identified a Pseudomonas prophage Sie protein that alters pilus dynamics through the pilus assembly chaperone, PilZ. This protein, known as Zip for Pil Z i nteracting p rotein, does not abrogate pilus activity, but fine tunes it, providing strong phage resistance without a fitness cost. This tuning is modulated through quorum sensing, which coordinates Zip production in concert with bacterial cell density to ensure maximal protection when bacterial populations are at the highest risk of phage infection. Most notably, Zip activity prevents internalization and destruction of phage progeny. We refer to this as the “anti-Kronos effect” after the Greek god who devoured his own children and show that it is a conserved feature of diverse prophage-encoded Sie systems.