Abstract
The ecological persistence of Bifidobacterium breve across life stages reflects adaptive strategies beyond the classical infant- versus adult-type dichotomy, historically attributed to differential nutrient utilization. Here, comparative genomics revealed no major differences in shared carbohydrate-related genes or accessory genome content between infant- and adult-derived strains. Instead, a distinct type III lanthipeptide bacteriocin cluster, lanKC, was specifically detected in adult-derived isolates. Functional assays combining gene knockout, in vitro co-cultivation, and human intervention demonstrated that lanKC enhances strain-level competitive fitness and promotes community stability. Phylogenetic and metagenomic analyses of 5,475 lanKC homologs and 6,122 infant gut metagenomes further suggested a possible early-life acquisition via intra-genus horizontal gene transfer. These findings uncover a previously unrecognized genetic basis underlying B. breve adaptation to the gut environment and support a multi-factorial model in which metabolic flexibility and interference competition jointly sustain bifidobacterial persistence and host-microbe symbiosis throughout life.