Dietary Bacillus amyloliquefaciens enhance survival of white spot syndrome virus infected crayfish

Bacillus amyloliquefaciens, which is closely related to Bacillus subtilis, produces a series of metabolites that can inhibit the growth of fungi and bacteria. Here, we investigated the effect of B. amyloliquefaciens used as a probiotic on the innate immunity of the crayfish Procambarus clarkii when challenged with white spot syndrome virus (WSSV). Dietary B. amyloliquefaciens supplement significantly reduced the mortality of WSSV-challenged crayfish and reduced copy numbers of WSSV. The quantitative reverse transcription-polymerase chain reaction results showed that B. amyloliquefaciens supplement increased the expression of several immune-related genes, including Toll-like receptor, NF-kappa B and C-type-lectin. Further analysis showed that B. amyloliquefaciens supplement also had an effect on three immune parameters, including total hemocyte count, phenoloxidase activity and superoxide dismutase activity. In both infected and uninfected crayfish, B. amyloliquefaciens supplement significantly decreased hemocyte apoptosis. Our results showed that B. amyloliquefaciens can regulate innate immunity of crayfish and reduce the mortality following WSSV challenge. This study provides a novel insight into the potential for therapeutic or prophylactic intervention with B. amyloliquefaciens to regulate crayfish immunity and protect against WSSV infection, and also provides a theoretical basis for the use of probiotics as aquatic feed additives.