A Small-Molecular-Weight Bacteriocin-like Inhibitory Substance (BLIS) UI-11 Produced by Lactobacillus plantarum HYH-11 as an Antimicrobial Agent for Aeromonas hydrophila

<i>Aeromonas hydrophila</i> is a typical pathogen that causes fish diseases and can easily infect different fish species. This study investigated the antibacterial activity, physicochemical properties and antibacterial mechanism of the BLIS UI-11 produced by <i>Lactobacillus plantarum</i> HYH-11, isolated from traditional kimchi in Hebei, China. It was found that BLIS UI-11 showed excellent inhibitory effect on the growth of <i>A. hydrophila</i>, and it also had a good antibacterial effect on various pathogens such as <i>Vagococcus fluvialis</i>, <i>Listeria monocytogenes</i>, <i>Aeromonas dhakensis</i>, <i>Aeromonas salmonicida</i>, <i>Salmonella Typhimurium</i>, <i>Escherichia coli</i> and <i>Staphylococcus aureus</i>. By measuring growth kinetics, it was found that the maximum antibacterial activity was reached after 30 h of culture, and both the optical density value at 600 nm (OD₆₀₀₎ and pH basically entered the stable phase after 20 h. Whole-genome analysis and gene cluster prediction identified a RiPP-like biosynthetic gene cluster, which comprises genes encoding precursor peptides, modification enzymes, and transport/immunity components. The molecular weight of the antimicrobial active substance was detected by dialysis and Tricine-SDS-PAGE, and it was shown to be an ultra-small molecular substance (<1 kDa). BLIS UI-11 was sensitive to protease K, but its antibacterial activity remained stable after treatment with acidic environment (pH 3.0-6.0), high-temperature treatment (121 °C for 30 min), and ultraviolet irradiation (4 h). After the sub-live cell assay (PI/SYTO9) and scanning electron microscopy (SEM), BLIS UI-11 inhibited the growth of bacteria by destroying the cell membrane of <i>A. hydrophila</i> to deform, collapse, and form holes that lead to accounting leakage. The hemolysis assay indicated that BLIS UI-11 exhibited incomplete hemolysis, suggesting its safety for application. The results showed that BLIS UI-11 produced by strain HYH-11 has great potential as an antimicrobial agent against <i>A. hydrophila</i> infection.