Symbiosis through lysis: prophage activation underlies Lactiplantibacillus plantarum probiotic function

The release of bacterial bioactive molecules across the gut barrier is a crucial yet poorly understood step in microbe-host communication. Here we unravel a phage-driven mechanism that enables this process in a nutritional symbiont. In Lactiplantibacillus plantarum NC8 (LpNC8), we identify a stress-inducible prophage, pp2, that undergoes genotoxic-stress-dependent activation and triggers holin-lysin-mediated lysis. This controlled lytic program produces phage particles together with extracellular, membrane-derived bacterial particles, and is strictly required for the ability of LpNC8 to promote juvenile growth in nutritionally challenged Drosophila melanogaster. Disruption of pp2-dependent lysis abolishes particle release in vitro and eliminates the growth-promoting effect in vivo, without altering bacterial abundance in the gut. The magnitude of phage release correlates with the extent of host growth promotion, indicating that prophage induction contributes to the export of symbiotic factors. These findings reveal prophage-induced lysis as a central and previously unrecognized mechanism by which a beneficial gut bacterium enhances host development under nutritional stress.