Antimicrobial Efficacy and Food Application Potential of Bacteriocins LL3 and LL4 from Traditional Dairy-Derived Lactococcus lactis

To combat foodborne pathogens like Salmonella, this study employed an activity-based screening followed by metagenomic mining of the active isolates to discover and characterize bacteriocins from Inner Mongolian dairy products. From the 15 active isolates, Lactococcus lactis D63 and D64 were identified as harboring a putative biosynthetic gene cluster (BGC) encoding 2 bacteriocins, LL3 and LL4. Both peptides form amphipathic α-helical structures that disrupt bacterial membranes, leading to intracellular leakage and cell death. They exhibited effective antimicrobial activity, particularly against Salmonella Typhimurium. Crucially, when applied in a simulated milk model under standard refrigeration (4°C), synthesized LL4 demonstrated robust preservative efficacy by effectively controlling S. Typhimurium, showing comparable performance to the commercial preservative Nisin. Genetic analysis revealed that this BGC exhibits low basal transcription under standard laboratory growth conditions and shares high homology with plasmid elements, suggesting it is a mobile genetic element acquired via horizontal gene transfer. This study presents LL3 and LL4 as promising natural preservatives and validates metagenomic mining as an efficient strategy for uncovering antimicrobial genes.