A phage-selective trigger hints at an SOS-independent mechanism of prophage induction by oxidative stress.

We identified a prophage-selective induction in poly-lysogenic Staphylococcus aureus induced by certain phenazines, such as pyocyanin, produced by Pseudomonas aeruginosa. Using a focused library of phenazines, we discovered that prophage induction correlates not with antibiotic activity but with the compounds' ability to undergo redox cycling and generate reactive oxygen species (ROS). Importantly, we demonstrated that strong oxidative agents alone could selectively induce one of multiple prophages harbored by the bacterial host. Based on these findings, we propose the High-Level Oxidative Stress (HiLOS) response as an SOS-independent mechanism of prophage induction.