| Summary: | 碩士 === 國立屏東科技大學 === 生物科技系 === 106 === In the present study, a protease and xylanase producing bacteria strain was isolated from the intestine tract of Nile tilapia (Oreochromis niloticus) and characterized as Rummeliibacillus stabekisii by 16S rDNA sequencing and biochemical properties analysis. To evaluate the efficacy of R. stabekisii on growth enhancement, immune modulation and intestinal microflora improvement in fish, Nile tilapia was fed with diet containing 1 x 106 CFU/g or 1 x 107 CFU/g of R. stabekisii for two months. The results showed that weight gain and feed efficiency of Nile tilapia fed 1 x 106 CFU/g of R. stabekisii were significantly increased compared with those of fish fed the control diet and 1 x 107 CFU/g of R. stabekisii. The phagocytic activity and respiratory burst activity of head kidney leukocytes as well as the serum lysozyme activity of R. stabekisii-fed Nile tilapia were significantly higher than those of fish fed the control diet. Real-time PCR results showed that the mRNA espression of immune-related genes such as IL-1, TNF- and TGF- was significantly increased in Nile tilapia fed administered R. stabekisii. The survival of the tilapia fed 1 x 106 CFU/g of R. stabekisii was significantly higher than that of control groups after 7 days of post-infection by Streptococcus iniae. The NGS analysis of intestinal microflora showed that the fed R. stabekisii can colonize intestine and improve intestinal microflora by increasing the amount of Bacillus genus. In addition, this application is the first study of R. stabekisii to immune modulation in aquaculture. These above results showed that feeding an appropriate amounts of R. stabekisii can enhance not only growth performance but also immunity of Nile tilapia. Thus, R. stabekisii is a potential probiotic can be used as biologicals in aquaculture for growth enhancement and immune modulation.
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