Clostridium autoethanogenum protein (CAP) is a new single-cell protein source originating from inactivated bacteria. An in vitro digestion experiment and an 8-wk growth experiment were conducted to evaluate the molecular weight distribution of the CAP hydrolysate, and the effects of dietary CAP levels on the growth performance, plasma parameters, hepatic and intestinal health, and the diversity of gut-adherent microbiota of largemouth bass (Micropterus salmoides). The fish (initial body weight of 47.99 ± 0.01 g) were fed diets where CAP gradually replaced 0% (CAP0), 12.5% (CAP12.5), 25% (CAP25), 37.5% (CAP37.5) and 50% (CAP50) of low-temperature steam dried anchovy fish meal (LTFM) in the diet. Results showed that the content of peptides below 1,000 Da in the CAP hydrolysate (0.56 mg/mL) was higher than that of the LTFM hydrolysate (0.48 mg/mL). Dietary CAP inclusion had no negative effect on growth performance, while whole-body lipid content significantly reduced in the CAP25 and CAP50 groups (P < 0.05). The plasma alanine aminotransferase activities and triglyceride concentrations in the CAP inclusion groups were significantly lower than those in the CAP0 group (P < 0.05). The plasma aspartate aminotransferase activity was significantly reduced in the CAP37.5 group (P < 0.05). The richness and diversity of the gut-adhesive microbiota and the proportion of Clostridium sensu stricto 12 in the CAP50 group were significantly higher than those in the CAP0 group (P < 0.05). Dietary CAP inclusion inhibited inflammatory responses by down-regulating the mRNA levels of interleukin 1β (IL1β), IL10 and transforming growth factor β1 (P < 0.05) in the liver. The mRNA levels of acetyl-CoA carboxylase 1 were significantly down-regulated in the CAP12.5, CAP25 and CAP37.5 groups (P < 0.05), while that of fatty acid synthase was significantly down-regulated in the CAP50 group (P < 0.05). These results demonstrate that dietary CAP inclusion could improve the hepatic and intestinal health of largemouth bass, and can be helpful to further develop CAP as a functional feed ingredient.

产醇梭菌蛋白（CAP）是一种来源于灭活细菌的新型单细胞蛋白来源。进行了体外消化实验和 8 周生长实验，以评估 CAP 水解物的分子量分布，以及日粮 CAP 水平对生长性能、血浆参数、肝脏和肠道健康以及肠道多样性的影响- 大口黑鲈的粘附微生物群（Micropterus salmoides）。鱼（初始体重为 47.99 ± 0.01 g）喂食 CAP 逐渐取代 0% (CAP0)、12.5% (CAP12.5)、25% (CAP25)、37.5% (CAP37.5) 和 50% (饲料中低温蒸汽干鳀鱼粉 (LTFM) 的 CAP50)。结果表明，CAP水解产物中1000 Da以下肽的含量（0.56 mg/mL）高于LTFM水解产物（0.48 mg/mL）。日粮添加 CAP 对生长性能没有负面影响，而 CAP25 和 CAP50 组全身脂质含量显着降低（P  < 0.05）。CAP 包含组血浆丙氨酸氨基转移酶活性和甘油三酯浓度显着低于 CAP0 组（P < 0.05)。CAP37.5组血浆天冬氨酸氨基转移酶活性显着降低（P  < 0.05）。CAP50组肠道黏附菌群的丰富度和多样性以及狭义梭菌12的比例均显着高于CAP0组（P  < 0.05）。膳食 CAP 通过下调肝脏中白细胞介素 1β ( IL1β )、IL10和转化生长因子 β1 ( P  < 0.05) 的 mRNA 水平来抑制炎症反应。CAP12.5、CAP25和CAP37.5组乙酰辅酶A羧化酶1的mRNA水平显着下调（P < 0.05)，而 CAP50 组脂肪酸合酶显着下调( P  < 0.05)。这些结果表明，日粮中添加 CAP 可以改善大口黑鲈的肝脏和肠道健康，并有助于进一步开发 CAP 作为功能性饲料成分。