Screening of Leuconostoc Strains with Antibacterial Activity from Fermented Vegetables and Mining of Bacteriocin Gene Cluster

In order to improve the safety and preservability of fermented vegetables, strain Leuconostoc mesenteroides AP7, with potent inhibitory effects on foodborne pathogens and bacteria causing paocai over-acidification, was selected from 8 Leuconostoc strains derived from traditional fermented vegetables in Yunnan, China. The main antimicrobial substance of AP7 was determined by eliminating the effects of organic acid and H₂O₂ and through protease sensitivity. The acid stability and thermal stability were analyzed and potential bacteriocin gene clusters were mined from the whole genome sequence of AP7. The results showed that the culture supernatant still had obvious antibacterial activity after excluding the influence of acid and H₂O₂, and after protease treatment, the antibacterial effect decreased significantly. It was speculated that the antibacterial substance in the concentrated culture supernatant was bacteriocin. The bacteriocin was sensitive to pH changes, had high thermal stability, and had a molecular weight of 6.51~14.4 kDa. Whole genome sequencing showed that the whole genome of AP7 contained 1 chromosome (1948310 bp) and 2 plasmids (37366 and 20698 bp), with a GC content of 37.7%. There was a gene cluster with Enterocin_X_chain_beta bacteriocin as the core. Its encoded product was predicted to be a positively charged hydrophilic stable protein, the secondary structure was dominated by α-helix, and the tertiary structure was mainly composed of loose peptide chains at both ends and an α-helix in the middle. In summary, the bacteriocin-producing Leuconostoc mesenteroides AP7 has excellent antibacterial properties and has the potential to be applied to the fermentation and preservation of acidic foods.