A bacterial site 2 protease contributes to RNA phage resistance by targeting phage lysis protein

Lytic phages culminate their lifecycle by causing lysis of the infected host cell. Despite extensive research on the molecular mechanisms of phage lysis, our understanding of anti-phage resistance mechanisms during the lysis stage remains less understood. Here, we demonstrated that MucP, a site 2 protease of Pseudomonas aeruginosa (PA), mitigates the activity of the RNA phage PP7 lysis protein (LP), which contains a transmembrane (TM) helix, suggesting that MucP act as a resistance mechanism against PP7-induced lysis. We identified an LP variant (LP*) having enhanced helical propensity due to P26L and S40L mutations, which was unaffected by MucP and exhibited killing activity against PA strains that are resistant to the wild type LP, with an inverse correlation between MucP activity and LP susceptibility. A PP7 mutant with LP* exhibited MucP-escaper phenotype such as discernable plaque formation on MucP-expressing cells. These results suggest that MucP targets the RNA phage LP at the TM helix in certain strains, providing a resistance function compromising phage lysis by utilizing an existing bacterial enzyme in PA. IMPORTANCEDespite the importance of cell lysis as the last stage of phage lifecycle, the factors influencing coordinated lysis remain elusive in the context of phage-bacteria interactions. Our study identifies MucP, a membrane protease in Pseudomonas aeruginosa (PA), as a resistance factor against the RNA phage PP7 by destabilizing its lysis protein (LP), with lower helical tendency at transmembrane (TM) domain. An LP variant with higher helical tendency exhibits strong killing activity against PA isolates, revealing an inverse correlation between MucP activity and LP susceptibility. Since MucP is a conserved protease in mucoid conversion of PA, we propose that MucP offers an intrinsic or passive defense or resistance mechanism against the RNA phage, whose activities vary among the diverse PA isolates.