Bacteria have evolved numerous systems to defend against bacteriophage (phage) infection and prevent their propagation. Among those systems are the abortive infection (Abi) systems, which inhibit phage replication by targeting the host, sometimes leading to cell death. They can be encoded by prophages, which are incorporated into the genome of the host bacterium and can induce lytic cycles following their activation. However, the prophages must ensure that their encoded defence systems do not inhibit their own propagation. In a recent study, Sargen and Helaine identify two anti-phage defence systems that are encoded within the Gifsy-3 prophage of Salmonella enterica subsp. enterica ser. Typhimurium 14028 and reveal a new mechanism whereby phage activity is detected during late stages of phage infection.

Next, the authors showed that RemS protected S. Typhimurium against the phage BTP1 when it was encoded on Gifsy-3 but not when it was encoded on Gifsy-1. They went on to analyse regions that distinguish Gifsy-3 from Gifsy-1 and showed that disrupting the region that encodes the Gifsy-3 lysis gene cassette reduced protection against phage infection, and deletion of both the lysis genes and remS led to a loss of protection. These results suggest that RemS and a component within the lysis gene cassette of Gifsy-3 work together to provide host defence.