Effects of Bacillus spp. on growth, gut microbiota compositions and immunity of sea cucumber ( Apostichopus japonicus )

The aim of this study was to determine the effects of Bacillus licheniformis CQN-12, B. amyloliquefaciens CQN-2, and B. subtilis CQN-39 originally isolated from the gut of a healthy sea cucumber (Apostichopus japonicus), on the growth performance, gut microbiota and immune response of sea cucumbers (A. japonicus). Sea cucumbers were fed a commercial pellet feed supplemented with B. licheniformis CQN-12, B. amyloliquefaciens CQN-2 or B. subtilis CQN-39 at different concentrations (0 (control), 107 and 109 CFU/g respectively), for 60 days. Our results revealed that that dietary B. licheniformis CQN-12 and B. amyloliquefaciens CQN-2 (107 CFU/g optimal concentration) enhanced growth performance, up-regulated innate immunity and altered microbial colonization in the gut of sea cucumbers whereas dietary B. subtilis CQN-39 had no significant effect. Furthermore, diets supplemented with an optimal concentration of B. licheniformis CQN-12 and B. amyloliquefaciens CQN-2 stimulated the mRNA expression of superoxide dismutase, lysozyme, and catalase. In conclusion, our study suggests that B. licheniformis CQN-12 and B. amyloliquefaciens CQN-2 could be used in feed supplements for healthier production of sea cucumbers in artificial farms.