Effects Of Probiotic Bacillus Cereus On Growth,nutrient Metabolism,Antioxidant And Inflammatory Response Of Crucian Carp

Our previous study suggested that probiotic Bacillus cereus exerted benefits on the health of Pengze crucian carp(Carassius auratus var.Pengze),whereas its regulation mechanism is far from understanding.Hence,the purpose of this research is to explore the mechanism of action of B.cereus.In this study,Pengze crucian carp was respectively fed with 109 cfu/kg of live and heated-inactivated B.cereus(CD and DCD groups),and fish in Control group fed the basic feed.The entire experiment period was 70 days.The results showed that both live and heated-inactivated B.cereus significantly improved the growth performance of Pengze crucian carp.Feeding live and inactivated B.cereus could affect the digestive capacity of the intestine by increasing activities of trypsin(Trypsin)and reducing lipase(LPS),and meanwhile improve the absorption area of the intestine by improving the intestinal morphological structure to promote nutrition absorption.In addition,live and inactivated B.cereus can improve liver function in term of a reduction in the content of serum alanine aminotransferase(ALT),while reducing in the content of urea nitrogen(BUM),blood ammonia(AMM),high density lipoprotein(HDL),and density lipoprotein(LDL)was detected in serum.Interestingly,live B.cereus significantly improved the liver's ability to synthesize bile acids(TBA),which in turn increased serum bile acid content.At the same time,live B.cereus significantly increased the activity of liver lipoprotein lipase(LPL),liver lipase(HL),and acetyl-CoA carboxylase(ACC),and then further improved hepatic lipid metabolism in Pengze crucian carp.On the other hand,the inactivated B.cereus significantly reduced the content of total cholesterol(TCHO)in liver tissue.In addition,live and inactivated B.cereus could further improve the carbohydrate metabolism process of Pengze crucian carp by affecting the glycolysis and gluconeogenesis of the liver.Live and inactivated B.cereus improved the immunity of Pengze crucian carp,and the results showed that live and inactivated B.cereus significantly upregulated the LZM mRNA level,and the live B.cereus over-induced IgM gene expression in intestinal tissue.Additionally,Live B.cereus significantly improved serum antioxidant status through an elevation in the activities of total suproxide dismutase(TSOD),catalase(CAT)and glutathione peroxidase(GPX)and the concentration of reduce glutathione(GSH),whereas only a significantly higher CAT activity was detected in fish fed heated-inactivated B.cereus,following by significant decrease in malondialdehyde(MDA)concentration in these two additive groups.Meanwhile,the intestinal antioxidant property was improved in two additive groups through the increase in CAT and GPX activities and GSH content together with a significantly lower MDA content.The gene expression analysis indicated that the improvement of intestinal antioxidant property appeared to be associated with Nrf2 signaling pathway via up-regulating the mRNA levels of target genes like CAT,GPX1.Besides,living and heated-inactivated B.cereus supplementation could inhibit intestinal inflammatory responses by suppressing the transcription of pro-inflammatory cytokine due to the regulation of antioxidant system by Nrf2 activation and inducing the overexpression of anti-inflammatory cytokine IL-10.Then,the intestinal barrier function in two B.cereus group was improved by up-regulating expression of tight junction protein genes like Claudin12,ZO1,and/or Occludin-like.These results revealed that probiotics B.cereus supplementation could promote the growth and further improve intestinal health by enhancing antioxidant capacity,suppressing inflammatory response,and improving intestinal barrier function of Pengze crucian carp through Nrf2 signaling pathway.