凝结芽孢杆菌缓解镉暴露导致的鲤鱼肠道屏障损伤的作用及机制

The heavy metal cadmium (Cd) is an environmental pollutant that causes adverse health effects in fish. Fish ingesting Cd-contaminated water and feed can cause the disruption of the intestinal barrier and further induces the amplification of Cd absorption. In recent years, there have been more and more studies on the use of probiotics to protect the body from the toxicity of heavy metals. However, there have been no reports about the use of Bacillus coagulans to prevent or alleviate fish damage caused by cadmium exposure. The previous experiment of the project applicant suggested that Bacillus coagulans had the potential to alleviate the intestinal barrier damage caused by cadmium exposure, but its alleviation effect and mechanism of action were not clear. In this project, we sought to evaluate the effects of Bacillus coagulans on alleviation intestinal barrier damage in common carp caused by cadmium exposure, and to test the hypothesis that the protection of the intestinal barrier by Bacillus coagulans is based on the characteristics of cadmium adsorption, regulation of intestinal flora and antioxidant activity. The results will help to explore the possibility of Bacillus coagulans as a feed additive to alleviate the cadmium toxicity of aquatic animals, and enrich the existing theory of cadmium toxicity prevention.

镉是一种对鱼类危害严重的有毒重金属。鱼类摄食镉污染水体及饲料会导致肠道屏障损伤，进而对机体产生严重危害。近年来，使用益生菌缓解机体重金属毒性损伤的研究受到广泛关注。然而，利用水产养殖常用益生菌--凝结芽孢杆菌缓解鱼类镉毒性损伤的研究尚处空白。项目申请人前期实验提示，一株分离自养殖池塘底泥的凝结芽孢杆菌SCC-19具有缓解镉暴露导致的鲤鱼肠道屏障损伤的潜力，其缓解效果及作用机制尚不明确。本项目通过建立体内暴露模型，在鲤鱼基础饲料中添加不同浓度的凝结芽孢杆菌SCC-19，探讨其缓解镉暴露导致的鲤鱼肠道屏障损伤的效果。通过体内和体外暴露模型，以凝结芽孢杆菌的镉吸附、调节肠道菌群和抗氧化活性等特性为切入点，初步解析其缓解镉暴露引起的鲤肠道屏障损伤的作用机制。研究结果有助于探索凝结芽孢杆菌作为一种饲料添加剂缓解水产动物镉毒性的可能性，丰富现有的水产动物镉毒性防治理论。

本项目探究一株分离自养殖池塘底泥的Bacillus coagulans SCC-19缓解镉暴露导致的黄河鲤肠道屏障损伤的作用效果及机制。体外研究结果表明，B. coagulans SCC-19具有较高的镉耐受（MIC=500mg/L）和镉去除(29.12%)能力。体内研究结果表明，基础饲料中添加108CFU/g B. coagulans SCC-19能够有效降低黄河鲤肠道、肝脏和头肾中镉含量，显著提高肠道紧密连接蛋白基因claudin-2,occluding和zonula occludens-1的表达量，显著降低血清和肠道二胺氧化酶(Diamine Oxidase，DAO )和乳酸(D-lactic acid，D-Lac)的含量；此外，B. coagulans SCC-19干预组黄河鲤总抗氧化能力(T-AOC)、超氧化物歧化酶(SOD)、过氧化氢酶(CAT)和谷胱甘肽过氧化物酶（GSH-Px）活性水平显著高于0.5mg/L的镉暴露组，而活性氧(ROS)、丙二醛(MDA)水平显著低于镉暴露组；肠道微生物测序结果表明B. coagulans SCC-19能够恢复因镉暴露导致的黄河鲤肠道微生物菌群紊乱。另外，研究发现B. coagulans SCC-19可以显著降低肠上皮细胞肌球蛋白轻链激酶(MLCK)水平和肌球蛋白轻链(MLC)磷酸化程度。综上所述，B. coagulans SCC-19可以通过镉吸附及其自身抗氧化和调节肠道菌群的能力而缓解镉暴露导致的黄河鲤肠道屏障损伤，这一过程与MLCK/p-MLC信号通路相关。本项目初步解析了B. coagulans SCC-19缓解镉暴露引起的黄河鲤肠道屏障损伤的作用机制。研究结果有助于探索凝结芽孢杆菌作为一种饲料添加剂缓解水产动物镉毒性的可能性，丰富现有的水产动物镉毒性防治理论。