一株后生元菌株的抑菌特性研究及其细菌素基因簇的挖掘

本文旨在筛选一株可拮抗中国大鲵源嗜水气单胞菌的后生元菌株，并对其进行抑菌特性的研究和细菌素基因簇的挖掘。以中国大鲵病原性嗜水气单胞菌（Aeromonas hydrophila, Ah2）为指示菌，筛选一株产细菌素乳酸菌株并评估其药敏特性；采用有机溶剂萃取法初步纯化菌株产细菌素；通过pH、温度和消化酶耐受性、贮藏稳定性、抑菌谱及最小抑菌（MIC）和杀菌浓度（MBC）共六类指标评价细菌素的抑菌特性；溶血反应与细胞毒性实验测试细菌素对Ah2的抑菌效果，经扫描电子显微镜初步探究细菌素的抑菌机制；经由紫外全波长扫描定性细菌素以及Tricine-SDS-PAGE电泳测定细菌素的分子量范围；最后根据菌株的全基因组序列挖掘其潜在的细菌素基因簇（RiPPs）。结果显示，从青岛市售腐乳中筛出一株产细菌素植物乳植物杆菌M4L1（Lactiplantibacillus plantarum M4L1）。初步纯化M4L1产细菌素并命名为LP01。细菌素LP01具备良好的消化酶耐受性，且在pH2~10、?20~121 ℃和9个月贮藏期内均表现出稳定的抑菌活性，并对单增李斯特菌、弗氏柠檬酸杆菌等14株革兰氏阳性和阴性菌均有不同程度的抑制作用；另外，LP01对Ah2的MIC和MBC分别为12.94和25.88 μg/mL。经MBC浓度的LP01处理后的Ah2，溶血活性和细胞毒性均得到明显缓解；SEM观察其通过破坏Ah2的细胞壁具有抑制或杀伤作用。LP01在波长200~220 nm处的肽类特征吸收峰显著，电泳后条带显示其分子量在3.3~4.0 kDa，LP01为小分子肽类细菌素。此外，基因注释到M4L1有2个细菌素基因簇（RiPPs），对应产物分别为Plantaricin K和Plantaricin E，均属于植物乳杆菌II类细菌素。菌株M4L1不仅含有多种抗菌物质相关基因簇，而且其细菌素LP01具备了优良的抑菌性能，能有效抑制多种水产病原菌、食物腐败菌及食源性致病菌等。产细菌素植物乳植物杆菌M4L1作为一株潜在的后生元菌株具有较好的应用前景。

Antimicrobial Properties of A Postbiotic Strain and Gene Cluster Mining of Its Bacteriocin

The aim of this study was to screen a postbiotic strain against Aeromonas hydrophila, and analyze its antibacterial characteristics and bacteriocin related gene cluster (RiPPs). The pathogen Aeromonas hydrophila (Ah2) from Andrias davidianus was used as an indicator for the screening of an excellent lactic acid bacterium (LAB), then the antibiotic susceptibility of the LAB to 10 common antibiotics was evaluated. The crude extract of bacteriocin (CEB) produced by the LAB was preliminarily purified by organic solvent extraction. Antibacterial properties of the CEB were then evaluated by 6 metrics below: pH, temperature and digestive enzyme tolerance, storage stability, antimicrobial spectrum, minimum inhibitory concentration (MIC) and maximum inhibitory concentration (MBC). CEB of two concentrations above was used for hemolysis and cytotoxicity experiment to further verify the bacteriocin’s effect on Ah2, and for scanning electron microscope (SEM) observation to preliminary explore the antimicrobial mechanism of the bacteriocin. Then through UV full-wavelength scanning and Tricine-SDS-PAGE, the qualitation and molecular weight of the bacteriocin was seprately identified and estimated. Finally, the whole genome sequence of the LAB was determined and then its potential bacteriocin gene cluster (RiPPs) mining was predicted in the core peptide database BAGEL4. Results showed that the excellent bacteriocin-producing strain M4L1 was isolated and screened from the Sufu sold in Qingdao, and was identified as Lactiplantibacillus plantarum (L. plantarum). The bacteriocin of L. plantarum M4L1 was half-purified and named as LP01. Bacteriocin LP01 exhibited good digestive enzyme tolerance and relatively stable antibacterial activity at pH2~12, ?20~121 ℃ and 9 months storage, it also presented a wide antimicrobial spectrum on 14 Gram positive and negative strains including 7 aquatic pathogens, such as Listeria monocytogenes, Citrobacter freundii and etc. Moreover, the MIC and MBC of LP01 against Ah2 was 12.94 and 25.88 μg/mL, respectively. After treatment with LP01, the hemolytic activity and cytotoxicity caused by Ah2 were significantly relieved as confirmed, which presented bacteriocin LP01’s excellent antibacterial effect. Especially, the SEM results showed that LP01 could inhibit or kill Ah2 by damaging cell wall. LP01 showed significantly characteristic peak at 200~220 nm corresponding to peptides, and electrophoresis band indicated the molecular weight range of LP01 was 3.3~4.0 kDa. LP01 was identified as small-peptide bacteriocin. There are 2 bacteriocin gene clusters (RiPPs) corresponding to the class II bacteriocins, L. plantarum Plantaricin K and Plantaricin E, were found in the genome of strain M4L1. In all, the bacteriocin-producing L. plantarum M4L1 not only owned bacteriocin gene clusters, but was also equipped with excellent antimicrobial characteristics and could inhibit a variety of aquatic pathogens, which has the potential to be developed as a postbiotic candidate strain in aquaculture.