Many　bacteria　in　nature　use　quorum　sensing　(QS)　to　regulate　gene　expression.　The　quorum　sensing　system　plays　critical　roles　in　the　adaptation　of　bacteria　to　the　surrounding　environment.　Previous　studies　have　shown　that　during　high-density　fermentation,　the　autolysis　of　lactic　acid　bacteria　was　regulated　by　the　QS　system,　and　the　two-component　system　(TCS,　LBUL_RS00115/LBUL_RS00110)　is　involved　in　the　autolysis　of　Lactobacillus　delbrueckii　subsp.　bulgaricus.　However,　the　QS　signal　molecule,　which　regulates　this　pathway,　has　not　been　identified.　In　this　study,　we　compared　the　genome　of　Lactobacillus　bulgaricus　ATCC　BAA-365　with　the　locus　of　seven　lactobacillus　QS　systems;　the　position　of　the　QS　signal　molecule　of　Lactobacillus　bulgaricus　ATCC　BAA-365　was　predicted　by　bioinformatics　tool.　Its　function　was　identified　by　in　vitro　experiments.　Construction　of　TCS　mutant　by　gene　knockout　of　LBUL_RS00115　confirmed　that　the　signal　molecule　regulates　the　density　of　the　flora　by　the　TCS　(LBUL_RS00115/LBUL_RS00110).　This　study　indicated　that　quorum　quenching　and　inhibition　based　on　the　signal　molecule　might　serve　as　an　approach　to　reduce　the　rate　of　autolysis　of　LAB　and　increase　the　number　of　live　bacteria　in　fermentation.