Microbial exopolysaccharides (EPS) from Lactococcus have been found to have an important role in the probiotic activity of this bacterium; however, the immunomodulatory and antioxidant activities have not been fully explored in aquaculture. In the present study, we investigated EPS-2 from Lactococcus lactis Z-2, isolated from healthy common carp, for its immunomodulatory and antioxidant effects and disease resistance against Aeromonas hydrophila in Cyprinus carpio L. We found that the molecular weight of EPS-2 was 18.65 KDa. The monosaccharide composition of this polymer was rhamnose, xylose, mannose, glucose, and galactose at a molar percentage of 13.3%, 14.1%, 18.5%, 27.4%, and 26.7%, respectively. EPS-2 treatment could modulate the immune responses in vitro and in vivo. In vitro tests showed that EPS-2 could significantly enhance the proliferation and phagocytosis activities (P < 0.05) as well as induce the production of nitic oxide (NO), pro-inflammatory cytokines (TNF-α, IL-1β, IL-6), and anti-inflammatory cytokines (IL-10, TGF-β) (P < 0.05) in head kidney cells. When the fish were gavaged with three different concentrations of EPS-2 (250, 500, 1000 μg/mL) for 7 days and infected with A. hydrophila, different expression patterns of the NO, cytokines, lysozyme (LZM), and alkaline phosphatase (AKP) in the serum and of antioxidants (T-AOC, SOD, CAT, GSH, GSH-Px and MDA) in hepatopancreas were observed. Before infection with A. hydrophila, EPS-2 supplementation significantly up-regulated the NO production, protein levels of pro-inflammatory cytokines (TNF-α, IL-1β, IL-6), LZM and AKP activities, and levels of antioxidant molecules compared to those in the negative (G1) group (P < 0.05), whereas levels of NO and pro-inflammatory cytokines and LZM and AKP activities were significantly lower than those in the positive (G2) group after infection (P < 0.05). However, whether infected or not, the expression levels of anti-inflammatory cytokines (IL-10, TGF-β) were significantly increased in the EPS-2 treatment groups (P < 0.05). These results indicate that EPS-2 has immunomodulatory and antioxidant effects on common carp, both in vitro and/or in vivo, and can be applied as a common carp feed supplement to enhance fish immunity and disease resistance against A. hydrophila.

中文翻译：

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乳酸乳球菌Z-2的胞外多糖对鲤鱼天然免疫反应，抗氧化活性和抗亲水性气单胞菌的抗病性的影响。

已经发现，来自乳球菌的微生物胞外多糖（EPS）在这种细菌的益生菌活性中具有重要作用。然而，在水产养殖中尚未充分探索其免疫调节和抗氧化活性。在本研究中，我们调查了从健康鲤鱼中分离的乳酸乳球菌Z-2的EPS-2的免疫调节和抗氧化作用以及对鲤鱼嗜水气单胞菌的抗病性。我们发现EPS-2的分子量是18.65 KDa。该聚合物的单糖组合物是鼠李糖，木糖，甘露糖，葡萄糖和半乳糖，其摩尔百分比分别为13.3％，14.1％，18.5％，27.4％和26.7％。EPS-2处理可以调节体内和体外的免疫反应。体外试验表明，EPS-2可以显着增强增殖和吞噬活性（P <0.05），并诱导产生一氧化氮（NO），促炎细胞因子（TNF-α，IL-1β，IL-6）。 ）和头肾细胞中的抗炎细胞因子（IL-10，TGF-β）（P <0.05）。当用三种不同浓度的EPS-2（250、500、1000μg/ mL）喂食鱼7天并感染了亲水性链球菌时，NO，细胞因子，溶菌酶（LZM）和碱性磷酸酶的表达方式不同观察到血清中的（AKP）和肝胰腺中的抗氧化剂（T-AOC，SOD，CAT，GSH，GSH-Px和MDA）。在感染嗜水链球菌之前，EPS-2的添加显着上调了NO的产生，促炎性细胞因子的蛋白质水平（TNF-α，IL-1β，IL-6），LZM和AKP活性，与阴性（G1）组相比，抗氧化剂分子水平（P <0.05），而感染后NO和促炎细胞因子以及LZM和AKP活性水平显着低于阳性（G2）组（ P <0.05）。但是，无论是否感染，EPS-2治疗组抗炎细胞因子（IL-10，TGF-β）的表达水平均显着升高（P <0.05）。这些结果表明EPS-2在体外和/或体内都对鲤鱼具有免疫调节和抗氧化作用，并且可以用作鲤鱼饲料补充剂以增强鱼的免疫力和对嗜水链球菌的抗病性。感染后，NO和促炎细胞因子，LZM和AKP活性水平明显低于阳性（G2）组（P <0.05）。但是，无论是否感染，EPS-2治疗组抗炎细胞因子（IL-10，TGF-β）的表达水平均显着升高（P <0.05）。这些结果表明EPS-2在体外和/或体内都对鲤鱼具有免疫调节和抗氧化作用，并且可以用作鲤鱼饲料补充剂以增强鱼的免疫力和对嗜水链球菌的抗病性。感染后，NO和促炎细胞因子，LZM和AKP活性水平明显低于阳性（G2）组（P <0.05）。但是，无论是否感染，EPS-2治疗组中抗炎细胞因子（IL-10，TGF-β）的表达水平均显着升高（P <0.05）。这些结果表明EPS-2在体外和/或体内都对鲤鱼具有免疫调节和抗氧化作用，并且可以用作鲤鱼饲料补充剂以增强鱼的免疫力和对嗜水链球菌的抗病性。05）。这些结果表明EPS-2在体外和/或体内都对鲤鱼具有免疫调节和抗氧化作用，并且可以用作鲤鱼饲料补品，以增强鱼的免疫力和对亲水链球菌的抗病性。05）。这些结果表明EPS-2在体外和/或体内都对鲤鱼具有免疫调节和抗氧化作用，并且可以用作鲤鱼饲料补充剂以增强鱼的免疫力和对嗜水链球菌的抗病性。