Prophages exploit bacterial communication to modulate antiviral defence

Bacteria possess a diverse array of defences that protect them from their viral predators, known as phages. While these defences provide a selective advantage in the presence of phage challenge, this is balanced by a potential fitness cost. We recently discovered that an integrated form of Pseudomonas phage, known as a prophage, encodes a protein that modulates the activity of a common phage receptor, the type IV pilus, through an interaction with the pilus assembly protein PilZ. This protein, known as Zip for PilZ interacting protein, does not abrogate pilus assembly, but fine tunes its activity, providing strong phage resistance without the evolutionary cost associated with loss of twitching motility. Like CRISPR-Cas defence, Zip expression from the prophage is controlled by quorum sensing. This allows the prophage to finely tune expression in concert with bacterial cell density, ensuring maximal protection when bacterial populations are at the highest risk of phage infection.