Postbiotics of Bacillus subtilis LCBS1 have beneficial effects on bullfrogs (Lithobates catesbeianus)

Our previous studies found live Bacillus subtilis LCBS1 could improve the utilization efficiency and intestinal health in bullfrog (Lithobates catesbeianus) fed the SM-based diet. However, non-viable probiotics may play the health benefits of probiotics. Therefore, 0.8% NaCl (negative control group, CG), LCBS1 live bacteria (positive control group, LB) and postbiotics from LCBS1 (heat-inactivated bacteria, HIB; cell-free extract, CE; cell-free supernatant, CS) were added to the SM-based diets and their effects on growth performance, immunity and intestinal health were evaluated in a 56 days feeding trial in bullfrog. Dietary supplement LB, HIB and CE significantly improved weight gain and feed efficiency. Meanwhile, apparent digestibility coefficients of protein were significantly increased, and the pH values of jejunum were significantly decreased in the HIB and CE groups compared with the CG, and indifferent with the LB group. Lower jejunum malondialdehyde concentration, and higher jejunum total antioxidant capacity and whole-body protein deposition in the HIB group were observed compared with the CG, and indifferent with the LB group. Dietary supplement LB and HIB significantly increased activities of lipase and protease in the jejunum, and serum complement 4 level and alkaline phosphatase activity. Higher jejunum il-4 expression in the LB and HIB groups, and lower jejunum tnf-& alpha; expression in the HIB, CE and CS groups were observed. Furthermore, the jejunal physical barrier was improved in the LB, HIB, and CE groups. Higher villus height, muscular thickness and zo-1 expression, lower serum diamine oxidase activity and D-lactate concentration in the LB, HIB and CE groups were observed than those of the CG. Relative abundance of potential probiotics including Prevotella_9, Lactococcus, and Cetobacterium was increased in the LB and HIB groups, accompanied by decreased the relative abundance of potentially pathogenic bacteria Mycoplasma. Overall, postbiotics of LCBS1 (heat-inactivated bacteria and cell-free extract) could be applied as a potential additive in bullfrog diet.