Abstract：
Probiotics as dietary additives can improve weight gain, feed efficiency, and disease resistance in cultured fish. In this research, we evaluated and compared the effects of Bacillus subtilis on immunity, mucosal tissue morphology, immune-related gene transcriptions, and intestinal microbiota in flounder (Paralichthys olivaceus) by a 30-day feeding experiment based on a continuous feeding schedule (E1) and a discontinuous feeding schedule (E2). As a result, the use of B. subtilis exerted the best positive effects on survival rate, enzyme activity, mucosal tissue morphology, immune-related gene transcriptions, and intestinal microbiota in flounders. Alkaline phosphatase (AKP), lysozyme (LZM), and superoxide dismutase (SOD) activities in the liver of E2 were higher than those of E1 (P < 0.05). Furthermore, the villi length in the intestinal tract and the fold length in the stomach of E2 were also higher than in E1 (P < 0.05). The il-1 expression levels in the spleen were significantly increased in E2 (P < 0.05) compared to E1. We performed 16 S rRNA sequencing analysis to find that Bacillus in E1 (1.06%) and E2 (1.01%) had higher relative abundances than in E0 (0.053%) at the end of the experiments, indicating that short-term application of B. subtilis with the continuous or discontinuous feeding method can allow both the adaptation of the ecosystem to the presence of probiotics by the establishment of new species in the gut microbiota and the ability these new probiotic species to perform corresponding functions. No significant differences in the ability of probiotic establishment were observed between E1 and E2. Our findings provided a unique perspective to explore the mechanism of immune enhancement with probiotics and to screen the optimal administration strategy in aquaculture application for probiotic use. Together, these results point to some level of enhancement in immune status by continuous and discontinuous feeding after a short-term feeding period, which could be used as a prophylactic strategy for flounder health management.
摘要：
益生菌作为膳食添加剂可以改善体重增加，饲料效率，和养殖鱼类的抗病性。在这项研究中,我们评估和比较了枯草芽孢杆菌对免疫的影响，粘膜组织形态学，免疫相关基因转录，通过基于连续饲喂时间表（E1）和不连续饲喂时间表（E2）的30天饲喂实验，以及比目鱼（Paralichthysolivaceus）的肠道微生物群。因此,枯草芽孢杆菌的使用对存活率产生了最好的积极影响，酶活性，粘膜组织形态学，免疫相关基因转录，和比目鱼的肠道微生物群。碱性磷酸酶(AKP),溶菌酶（LZM），E2和肝脏超氧化物歧化酶（SOD）活性高于E1（P<0.05）。此外，E2的肠道绒毛长度和胃中的褶皱长度也高于E1（P<0.05）。与E1相比，E2在脾脏中的il-1表达水平显着增加（P<0.05）。我们进行了16SrRNA测序分析，发现在实验结束时，E1（1.06%）和E2（1.01%）中的芽孢杆菌相对丰度高于E0（0.053%），这表明采用连续或不连续饲喂方法短期施用枯草芽孢杆菌既可以通过在肠道微生物群中建立新物种来使生态系统适应益生菌的存在，也可以使这些新的益生菌物种具有执行相应功能的能力。在E1和E2之间没有观察到益生菌建立能力的显著差异。我们的研究结果提供了一个独特的视角来探索益生菌的免疫增强机制，并筛选在水产养殖中应用益生菌的最佳给药策略。一起,这些结果表明，在短期喂养期后，通过连续和不连续的喂养，免疫状态有一定程度的增强，这可以作为比目鱼健康管理的预防策略。
