Functional ingredients such as Bacillus subtilis are used in aquaculture to improve fish condition, modulate microbiota and promote a healthy intestinal system. However, the underlying mechanisms of grass carp treated with B. subtilis are not fully characterized. This study investigated the gut microbes of grass carp after treated with B. subtilis H2 (10⁶ CFU/mL) and Aeromonas hydrophila (10⁶ CFU/mL). The intestinal flora was found that the dominant bacterial phyla identified in all samples were Proteobacteria, Actinobacteria, Fusobacteria, Bacteroidetes and Acidobacteria. Compared with the control group, the relative abundance of Proteobacteria and Bacteroidetes in B. subtilis group were significantly increased. In addition, the relative abundances of Aeromonas and Shewanella in A. hydrophila group were more than the control group. For the intestinal transcriptomic profiling of the grass carp treated with B. subtilis H2, 824 different expressed genes (DEGs) between the B. subtilis H2 treated and non-treated groups were detected, including 365 up-regulated and 459 down-regulated genes. Six DEGs were randomly selected for further validation by quantitative real-time RT-PCR (qRT-PCR) and the results were consistent with the RNA-seq data. Additionally, eight immunomodulatory genes (IL-4, IL-11, IFN-α, CSF, FOSB, MAPK12b, IGHV3-11 and IGHV3-21) were significantly up-regulated after treated with B. subtilis H2. Furthermore, almost all the lipid metabolism-associated genes were significantly up-regulated after treated with B. subtilis H2 according to the lipid metabolism pathways. Eleven lipid metabolism-associated genes were selected by qRT-PCR, which showed that the expressions of almost all the selected genes were increased, especially Apob-48, ABCG8 and DGAT. Taken together, our results support that B. subtilis could modulate the immune response, fat metabolism and bacterial assembly in the gut of grass carp.

枯草芽孢杆菌等功能性成分用于水产养殖，以改善鱼类状况，调节微生物群并促进健康的肠道系统。但是，用枯草芽孢杆菌处理的草鱼的潜在机制尚未完全阐明。本研究调查了枯草芽孢杆菌H2（10 ⁶  CFU / mL）和嗜水气单胞菌（10 ⁶  CFU / mL）处理后草鱼的肠道微生物。肠道菌群被发现，所有样品中鉴定出的优势细菌菌群是变形杆菌，放线菌，梭菌，拟杆菌和酸性细菌。与对照组相比，相对丰度变形菌和拟杆菌在枯草芽孢杆菌组显著增加。此外，的相对丰度气单胞菌和希瓦氏菌在嗜水组比对照组更大。对于处理的草鱼的肠转录谱枯草杆菌H2，824不同表达的基因之间（DEGS）枯草芽孢杆菌检测了H2治疗组和未治疗组，包括365个上调基因和459个下调基因。通过定量实时RT-PCR（qRT-PCR）随机选择了六个DEG，以进行进一步验证，结果与RNA-seq数据一致。此外，用枯草芽孢杆菌H2处理后，八个免疫调节基因（IL-4，IL-11，IFN-α，CSF，FOSB，MAPK12b，IGHV3-11和IGHV3-21）显着上调。此外，枯草芽孢杆菌处理后，几乎所有与脂质代谢相关的基因均显着上调。H2根据脂质代谢途径。通过qRT-PCR选择了11个脂质代谢相关基因，表明几乎所有选择的基因的表达都增加了，特别是Apob-48，ABCG8和DGAT。综上所述，我们的结果支持枯草芽孢杆菌可调节草鱼肠道中的免疫反应，脂肪代谢和细菌装配。