Administration of the Potential Probiotic Paenibacillus ehimensis NPUST1 Enhances Expression of Indicator Genes Associated with Nutrient Metabolism, Growth and Innate Immunity against Aeromonas hydrophila and Streptococcus indie Infections in Zebrafish (Danio rerio)

Probiotics as antibiotic alternatives for preventing and controlling infectious diseases are a relatively eco-friendly strategy in aquaculture. The bacteriocin-producing probiotic Paenibacillus ehimensis NPUST1 was isolated from tilapia culture pond water in our previous study. The present study demonstrated that P. ehimensis NPUST1 produced hydrolytic enzymes, including protease, amylase, cellulase, xylanase and lipase. The effects of P. ehimensis NPUST1 on zebrafish nutrient metabolism, growth performance and innate immunity were evaluated by measuring the expression of indicator genes in zebrafish after feeding P. ehimensis NPUST1 at doses of 106 and 107 CFU/g for 8 weeks. There was an obvious increase in the hepatic mRNA expression of carbohydrate metabolism-related genes, including glucokinase, hexokinase 1, glucose-6-phosphatase, and pyruvate kinase, and growth-related genes, including the growth hormone receptor and insulin-like growth factor-1. The expression of the innate immune-related genes including interleukin (IL)-1β, IL-6, IL-15, tumor necrosis factor-α, toll-like receptor (TLR)-1, TLR-4, complement component C3b and lysozyme were significantly increased in P. ehimensis NPUST1-supplemented fish. A significant reduction in cumulative mortality was exhibited in P. ehimensis NPUST1-supplemented fish after infection with Aeromonas hydrophila and Streptococcus iniae. In conclusion, our data suggested that P. ehimensis NPUST1 supplementation in feed could potentially improve nutrient metabolism and growth in addition to enhancing innate immunity and disease resistance against A. hydrophila and S. iniae in zebrafish.