Effect of mixed-Bacillus spp isolated from pustulose ark Anadara tuberculosa on growth, survival, viral prevalence and immune-related gene expression in shrimp Litopenaeus vannamei

The widespread overuse of antibiotics in aquaculture has led to the emergence of antibiotic-resistance shrimp pathogens, the negative impact on shrimp gut microbiota, and the presence of antimicrobial residues in aquaculture products, with negative consequences on human health. Alternatively, probiotics have positive effects on immunological responses and productive performance of aquatic animals. In this study, three probiotic bacteria, (Bacillus licheniformis MAt32, B. subtilis MAt43 and B. subtilis subsp. subtilis GAtB1), isolated from the Anadara tuberculosa were included in diets for juvenile shrimp, Litopenaeus vannamei, to evaluate their effects on growth, survival, disease prevalence, and immune-related gene expression. Shrimp naturally infected with WSSV and IHHNV were fed with the basal diet (control, T1) and diets supplemented with four levels of bacilli probiotic mix (1:1:1) at final concentration of (T2) 1 × 106, (T3) 2 × 106, (T4) 4 × 106, and (T5) 6 × 106 CFU g−1 of feed. The specific growth rate of shrimp was significantly higher in T2 than in T1 (control) treatment, and the final growth as well as the survival were similar among treated groups. The prevalence of WSSV and IHHNV infected shrimp was reduced in T2 and T4 treatments, respectively, compared with control. The mRNA expression of proPO gene was higher in treatment T4 than control. The LvToll1 gene was significantly up-regulated in treatments T4 and T5 compared to control. The SOD gene was up-regulated in treatment T5 compared to control. In contrast, the mRNA expression of the Hsp70 gene was down-regulated in treatments T4 and T5 respect to control, and the TGase gene remained unaffected by the level of bacillus probiotic mix. As conclusion, the bacilli probiotic mix (Bacillus spp.) enhanced immune-related gene expression in WSSV and IHHNV naturally infected shrimp. This is the first report of probiotic potential of bacteria isolated from A. tuberculosa on the immune response and viral prevalence in shrimp Litopenaeus vannamei. •Combined Bacillus probiotic strains can increase the specific growth rate of shrimp.•The bacillus probiotic mix can help in reducing the natural prevalence of WSSV and IHHNV infected shrimp.•The bacillus probiotic mix in naturally WSSV and IHHNV infected shrimp can modulate immune-related genes.•Probiotic bacteria from A. tuberculosa enhance the immune response in shrimp.