Similar mechanisms of retron-mediated anti-phage defense for different families of tailed phages

Summary Bacterial retrons are tripartite systems consisting of a cognate non-coding RNA, reverse transcriptase, and additional (effector) protein with diverse predicted enzymatic functions. In this study, we investigated the role and mechanism of Retron-Eco11, a novel type III-A3 retron system associated with a phosphoribosyltransferase-like effector protein, in phage defense. Here, we show that the Retron-Eco11 tripartite system protects against phage infection and that UvsW and D10, two functional homolog helicases found in T4 and T5 phages, respectively, serve as specific triggers for the Retron-Eco11 defense system. Our findings confirmed that msDNA and both protein components of the intron complex are indispensable for its protective function. Once the retron system detects the activity of these helicase proteins, it activates the toxicity of the effector protein bound to the retron complex, leading to an abortive infection. These findings underscore the application of a comparable anti-phage defense strategy using Retron-Eco11 across diverse phage families. This should aid in deciphering the processes through which the Retron complex detects and identifies the invading phages.