Bacillus coagulans SCC-19 maintains intestinal health in cadmium-exposed common carp (Cyprinus carpio L.) by strengthening the gut barriers, relieving oxidative stress and modulating the intestinal microflora

Heavy metal cadmium (Cd) pollution is a serious problem affecting the sustainable development of aquaculture and the safety of aquatic foods. Research about the use of probiotics to attenuate toxic damage caused by Cd²⁺ in aquatic animals has received widespread attention. Bacillus coagulans (B. coagulans), a kind of probiotics commonly used in aquaculture, has been shown to adsorb Cd²⁺ both in vivo and vitro. Here, we aimed to determine the effects of B. coagulans on Cd²⁺ bioaccumulation, gut barrier function, oxidative stress and gut microbiota in common carp following Cd²⁺ exposure. The fish were exposure to Cd²⁺ at 0 and 0.5 mg/L and/or fed a B. coagulans-containing diet at 10⁷, 10⁸ and 10⁹ CFU/g for 8 weeks. The results indicated that B. coagulans can maintain gut barrier function in Cd²⁺-exposed fish by reducing Cd²⁺ bioaccumulation, increasing the mRNA levels of tight junction protein genes (occludin, claudin-2 and zonula occludens-1), and decreasing the levels of diamine oxidase and D-lactic acid. In addition, B. coagulans could relieve oxidative stress in Cd²⁺-exposed fish by restoring the activities of glutathione peroxidase, catalase and superoxide dismutase. Moreover, Cd²⁺ exposure decreased the intestinal microbiota diversity and changed the intestinal microbiota compositions in common carp. However, supplementation with B. coagulans could reverse the altered intestinal microbiota diversity and composition after Cd²⁺ exposure, decrease the abundance of some pathogens (Shewanella and Vibrio), and increase the abundance of probiotics (Bacillus and Lactobacillus). These results indicate that B. coagulans may serve as a potential antidote for alleviating Cd²⁺ toxicity.