This study aimed at evaluating the effects of dietary inclusion of Bacillus subtilis DSM 32315 on the growth, immunity, intestinal architecture and gut microbiota of juvenile largemouth bass Micropterus salmoides (LMB). B. subtilis DSM 32315 was supplemented in the diets at the levels of 0 (control, CON), 1.5 (BS1.5, 3 × 10⁶ CFU/g feed) and 3 g/kg (BS3, 6 × 10⁶ CFU/g feed). Each diet was assigned to four replicate tanks of LMB juveniles (initial mean body weight, 8.32 ± 0.06 g) with 20 fish per tank for 9 weeks. The results showed that the growth and feed utilization of LMB were not sensitive to dietary modifications (p > .05). Compared with the CON fish, dietary BS supplementation did not affect the haematological parameters (white and red blood cell counts and haematocrit value) of LMB (p > .05), but the BS1.5 fish performed better than the BS3 fish. Serum innate immunity indicators (lysozyme activity and complement C3 and C4 levels) were improved with dietary BS supplementation at both doses, while higher serum IgM level was only recorded at 1.5 g/kg feed (p < .05). All the sampled fish exhibited intact intestines, but the intestinal architecture (villus height and muscular layer thickness) still benefited from dietary BS inclusion at both doses (p < .05). Although intestinal anti-inflammatory response (mRNA levels of IL-10 and TGF-β1) did not differ between the BS supplemented fish (p > .05), the BS1.5 fish obtained superior pro-inflammatory response (mRNA levels of IL-1β, IL-8, and TNF-α) over the BS3 fish (p < .05). Compared with the CON fish, the abundance of the harmful Plesiomonas shigelloides decreased in the gut microbiota of the BS1.5 fish (p < .05). Despite the BS3 fish obtained higher diversity of gut microbiota, the abundances of potential beneficial (Cetobacterium somerae and Shewanella xiamenensis) and harmful bacteria (Acinetobacter johnsonii and P. shigelloides) increased or decreased simultaneously (p < .05). Taken together, it was concluded that dietary BS DSM 32315 inclusion presented some positive effects on LMB. Although the BS1.5 fish performed better than the BS3 fish, the best supplemental dose need to be further studied.

中文翻译：

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日粮中添加枯草芽孢杆菌 DSM 32315 对大口黑鲈幼鱼生长、免疫和肠道形态、微生物群和炎症反应的影响

本研究旨在评估日粮中添加枯草芽孢杆菌DSM 32315 对幼年大口黑鲈 (LMB) 的生长、免疫、肠道结构和肠道微生物群的影响。乙。 日粮中添加枯草杆菌DSM 32315 的水平为 0（对照，CON）、1.5（BS1.5，3 × 10 ⁶  CFU/g 饲料）和 3 g/kg（ BS3，6 × 10 ⁶ CFU/g 饲料） ）。每种饲料被分配到 LMB 幼鱼的四个重复池（初始平均体重，8.32 ± 0.06 g），每个池 20 条鱼，持续 9 周。结果表明，LMB的生长和饲料利用率对日粮改良不敏感（p > .05)。与 CON 鱼相比，日粮中添加 BS 对 LMB 的血液学参数（白细胞和红细胞计数和血细胞比容值）没有影响 ( p  > .05)，但 BS1.5 鱼的表现优于 BS3 鱼。血清先天免疫指标（溶菌酶活性和补体 C3 和 C4 水平）在两种剂量的日粮中添加 BS 均得到改善，而血清 IgM 水平仅在 1.5 g/kg 饲料时出现（p  < .05）。所有采样的鱼都表现出完整的肠道，但肠道结构（绒毛高度和肌肉层厚度）仍然受益于两种剂量的日粮 BS ( p  < .05)。虽然肠道抗炎反应（IL - 10的 mRNA 水平和TGF - β1 ）在补充BS的鱼之间没有差异（p > .05）， BS1.5鱼获得了优于BS3 鱼 ( p  < .05)。与 CON 鱼相比，BS1.5 鱼肠道菌群中有害菌类志贺单胞菌的丰度降低( p  < .05)。尽管 BS3 鱼获得了更高的肠道微生物群多样性，但潜在有益菌（Cetobacterium somerae和Shewanella xiamenensis）和有害细菌（Acinetobacter johnsonii和P. shigelloides  ）同时增加或减少（p  <.05）。总之，得出的结论是，膳食 BS DSM 32315 对 LMB 有一些积极影响。虽然 BS1.5 鱼的表现优于 BS3 鱼，但最佳补充剂量需要进一步研究。