Xylanase Improves the Intestinal Barrier Function of Nile Tilapia(oreochromis Niloticus)fed with Soybean(glycine Max)meal

Background Soybean(Glycine max)meal is one of the important protein sources for fish,but the non-starch polysac-charides(NSP)in soybean meal impair the intestinal barrier function.Here we aimed to investigate whether xylanase can alleviate the adverse effects on the gut barrier induced by soybean meal in Nile tilapia and to explore the possible mechanism. Results Nile tilapia(Oreochromis niloticus)(4.09±0.02 g)were fed with two diets including SM(soybean meal)and SMC(soybean meal+3,000 U/kg xylanase)for 8 weeks.We characterized the effects of xylanase on the gut barrier,and the transcriptome analysis was performed to investigate the underlying mechanism.Dietary xylanase improved intestinal morphology and decreased the concentration of lipopolysaccharide(LPS)in serum.The results of transcrip-tome and Western blotting showed that dietary xylanase up-regulated the expression level of mucin2(MUC2)which may be related to the inhibition of protein kinase RNA-like endoplasmic reticulum kinase(perk)/activating transcrip-tion factor 4(atf4)signaling pathways.Microbiome analysis showed that addition of xylanase in soybean meal altered the intestinal microbiota composition and increased the concentration of butyric acid in the gut.Notably,dietary sodium butyrate was supplemented into the soybean meal diet to feed Nile tilapia,and the data verified that sodium butyrate mirrored the beneficial effects of xylanase. Conclusions Collectively,supplementation of xylanase in soybean meal altered the intestinal microbiota composi-tion and increased the content of butyric acid which can repress the perk/atf4 signaling pathway and increase the expression of muc2 to enhance the gut barrier function of Nile tilapia.The present study reveals the mechanism by which xylanase improves the intestinal barrier,and it also provides a theoretical basis for the application of xylanase in aquaculture.