| Probiotics have received much attention as novel dietary supplements for antibiotic substitution in aquaculture. In particular, brewer’s yeast, Saccharomyces cerevisiae, has been used as probiotics in various aquatic species, and beneficial effects of brewer’s yeast as probiotics include growth promotion, enhancement of innate immune response, as well as protection against pathogens infection. This dissertation was aimed to investigate the effects of dietary Saccharomyces cerevisiae live cells or heat-inactivated yeast on juvenile Nile tilapia(Oreochromis niloticus L.) in high density culture model cases or supplement to two practically popular basal diets with difference in protein sources(fish meal diets A and soybean meal diets B). Contents of the research were containing growth performance, gut mucosal morphology and/or gut digestive enzyme(amylase, lipase and protease), immune response(hsp70 and cytokine expression of intestine and head kidney), gut adhesive/non-adhesive bacterial community and disease resistance of juvenile Nile tilapia.we also investigate the effects of dietary Saccharomyces cerevisiae culture or live cells with Bacillus amyloliquefaciens spores on growth performance, gut mucosal morphology, hsp70 gene expression, and disease resistance of juvenile common carp(Cyprinus carpio)The Nile tilapia with similar size were randomly chosen and distributed into 12 tanks at a density of 24 fish per tank(4.12g/L) which were supplemented by 1g/kg live S. cerevisae(LY, produced by Lesaffre, France) or 1g/kg heat-inactivated S. cerevisae(HIY) or no yeast supplemention(CK), and other 4 tanks at 12 fish per tank(2.06g/L).had not yeast supplemention(Low CK) The experiment was conducted in aquaria for 8 weeks. Results showed that the growth performances were not significantly improved in all treatment groups(P > 0.05). Intestinal mucosal morphology analysis indicated that the intestinal microvilli length in treatment LY was significantly higher compared to CK(P < 0.05) but Low CK(P > 0.05), while no significant difference was observed intestinal microvilli density was observed in all treatment groups(P > 0.05). The gut digestive enzyme analysis indicated trypsin-specific activity was significantly increased in LY and HIY compared to CK and Low CK, while no significant difference was observed in amylase activity and lipase activity. The expression of the gene involved in animal welfare(HSP70) and cytokine were analyzed. No significant difference in hsp70 and tgf-β gene expression was observed in intestine for different dietary groups; il-1β expression was significantly up-regulated(P < 0.05) compared to Low CK but not CK; tnf-α expression was significantly up-regulated(P < 0.05) compared to Low CK and CK. In head kidney, compared with CK the, hsp70 expression was decreased in LY(P < 0.05) but not Low CK, meanwhile in il-1β the expression was significantly up-regulated(P < 0.05) compared to CK and Low CK. However, no significant difference was observed in tnf-α and tgf-β expression among all treatment groups. The alkaline phosphatase activity significantly reduced in LY and Low CK compare to CK while no significant difference was observed in HIY showed LY some protection against A. hydrophila infection in Nile tilapia. Intestinal microbiota of hybrid tilapia analysis: For the allochthonous microbiota, these three taxa dominated the community composition and maintained a relatively stable community composition in all treatments, represented by Fusobacteria, Proteobacteria and Actinobacteria, and microflora of Fusobacteria almost composed of Fusobacteriaceae. For the autochthonous microbiota, we observed two taxa dominated microbial community composition, represented by Fusobacteria and Proteobacteria. Compared with allochthonous microbiota, the percentage of Actinobacteria was reduced in all treatments. Furthermore, the percentage of Proteobacteria was increased in LY compare to CK and Low CK, but not in HIY; in contrast, the percentage of Fusobacteria was reduced. As the similar result, the percentage of Enterobacteriaceae was increased in LY compare to CK and Low CK by family level, Correspondingly, the percentage of Fusobacteriaacese was reduced by family level. In conclusion, live S. cerevisae may confer some beneficial effect to Nile tilapia, as indicated by the improved gut microvilli length, higher trypsin-specific activity and reduced hsp70 expression level in head kidney, as well as for protection against A. hydrophila infection to Nile tilapia.In this study section, the involvement and extent of contribution of secretory metabolites to the probiotic effects of brewer’s yeast was investigated in Nile tilapia. Equal dose of live and heat-inactivated brewer’s yeast(devoid of secretory metabolites) was supplemented to two basal diets. Fish were fed with each diet for 8 weeks. Growth, feed utilization, gut microvilli morphology, and expressions of hsp70 and inflammation-related cytokines in the intestine and head kidney were assessed. Intestinal microbiota was investigated with 16 S r RNA gene pyrosequencing. Gut alkaline phosphatase(AKP) activity was measured after challenge of fish with Aeromonas hydrophila. Results showed that live yeast improved FBW(P < 0.05), WG(P < 0.05), and FCR(P = 0.06) of fish compared with control. No significant differences were observed between inactivated yeast and control. Live yeast improved gut microvilli length(P < 0.001) and density(P < 0.05) while inactivated yeast didn’t. The hsp70 expression level in both intestine and head kidney of fish was significantly reduced by live yeast(P < 0.05), while no significant differences were registered for inactivated yeast. Live yeast reduced intestinal expression of tnf-α(P < 0.05), tgf-β(P < 0.05 under diet A) and il-1β(P = 0.08), while no significant effect was observed for inactivated yeast. Both live and inactivated yeast exerted subtle influence on the intestinal microbiota of fish. Intestinal Lactococcus spp. was enriched by live and inactivated yeast. Lastly, both live and inactivated yeast reduced the gut AKP activity compared with control(P < 0.001), indicating protection of the host against infection by A. hydrophila. In conclusion, secretory metabolites didn’t play major roles in the growth promotion and disease protection effects of yeast. Nevertheless, secretory metabolites were the major contributing factor towards improved gut microvilli morphology, relieved stress status, and reduced intestinal inflammation of Nile tilapia fed diets supplemented with brewer’s yeast as probiotics.Four practical diets were formulated, i.e. control diet, diet Y1(supplemented with1g/kg Saccharoculture, a Korean-made S. cerevisae culture product containing 107 CFU/g B. amyloliquefaciens spores), diet Y2(supplemented with 2 g/kg S. cerevisae culture, DVAQUA®,produced by Diamond V Mills Inc., IA, USA, as the positive control) and diet Y3(supplemented with Changlijian, a local product with each gram containing 1010 CFU live S. cerevisae cells and 1.2 × 1010 CFU B. amyloliquefaciens spores, at the recommended dose of 0.2 g product per kg feed). Each diet was randomly assigned to triplicate groups of 12 fish. The experiment was conducted in aquaria for 8 weeks. Results showed that the growth performances were not significantly improved in all treatment groups. Intestinal mucosal morphology analysis indicated that the posterior intestinal microvilli length in treatment Y1 and Y2 was significantly increased compared to control(P < 0.05), while significantly reduced posterior intestinal microvilli density was observed in Y3(P < 0.05). The expression of the gene involved in animal welfare(70KDa-Heat Shock Protein gene) was analyzed. No significant difference in hsp70 gene expression was observed in intestine for different dietary groups. In liver, the expression was decreased in Y1 and Y2, while in Y3 the expression was significantly increased(P < 0.05). However, the expression was significantly up-regulated in kidney for Y2. Lastly, all treatment groups showed some trend of protection against A. hydrophila infection in common carp. In conclusion, lower level of S. cerevisae culture with B. amyloliquefaciens spores(1 g/kg Saccharoculture) may confer some beneficial effect to common carp, but the supplementation of live S. cereviase cells with B. amyloliquefaciens spores didn’t provide any improvements under the present experimental conditions. |
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