Paenibacillus polymyxa improves the growth, immune and antioxidant activity, intestinal health, and disease resistance in Litopenaeus vannamei challenged with Vibrio parahaemolyticus

Abstract

This present study was performed to examine the effects of different levels of dietary Paenibacillus polymyxa ATCC 842 (PP) on the growth, immune response, antioxidant activities, intestinal morphology and microbiota, and defense against Vibrio parahaemolyticus (VP) infection in white leg shrimp, Litopeneaus vannamei. Shrimps (initial weight of 0.58 ± 0.001 g) were fed diet containing 0 (control, PP0), 106 (PP1), 107 (PP2) and 108 (PP3) cfu g−1P. polymyxa. After 8 weeks feeding trial, shrimps fed the PP treated diet displayed a synergistic effect which significantly enhanced (P < 0.05) the final body weight, survival rate, weight gain rate, specific growth rate, protein efficiency ratio, condition factor; total protein, albumin, globulin, triglyceride, lysozyme, total antioxidant capacity, superoxide dismutase, acid phosphatase activity in the serum; alkaline phosphatase activity in the hepatopancreas; glutathione, glutathione peroxidase activity in both the serum and hepatopancreas, with decreased feed conversion rate; aspartate aminotransferase, alanine aminotransferase, and malondialdehyde levels in both serum and hepatopancreas compared to the control group (PP0). Correspondingly, the probiotic-treated group experienced significantly improved (P < 0.05) mid-intestinal morphological structures such as villi height, villi width, muscle thickness and digestive enzyme activities including amylase, trypsin, and lipase than the untreated group with the PP3 group obtaining the highest. Dietary PP supplementation in diets again was observed to change the shrimps' intestinal microbial composition. Explicitly, the most dominant bacterial phyla, Proteobacteria, Bacteriodetes, and Planctomycetes observed in this study were significantly higher (P < 0.05) in the probiotic-enriched group compared to the control. At the genus level, the relative abundance of opportunistic bacterial pathogens (Vibrio, Photobacterium, Tenacibaculum, and Shewanella) were significantly decreased (P < 0.05), whereas beneficial bacteria (Ruegeria and Pseudoalteromonas) were significantly enhanced (P < 0.05) in the probiotic-treated group than the untreated. Additionally, dietary supplementation of PP in L. vannamei's diet significantly improved (P < 0.05) the protection against VP infections with PP3 treatment group obtaining the highest relative percentage survival of 78.3%. These results collectively suggest that dietary PP had a positive effect on the intestinal health of L. vannamei via the modulation of the microbial composition; thus, promoting the digestion and absorption of nutrients in boosting shrimps' immunity. The optimal supplementation dosage in diets was found to be 108 cfu g−1 diet.