Characterization of the Antimicrobial Peptides Gene of Bacillus subtilis in the Intestine of Common Carp and Its Relationship with Toll-Like Receptor Expression in the Kidney and Liver

Bacillus subtilis is recognized as a probiotic bacterium with the potential to enhance fish immunity through the production of antimicrobial peptides (AMPs). This study evaluated a strain of B. subtilis isolated from fish intestines in previous research, designated as Bacillus CgM22, which has the potential to act as a probiotic and immunostimulant. Therefore, further research is needed to analyze the AMPs gene in Bacillus CgM22 at the molecular level and to assess the expression of the toll-like receptor (TLR2) gene in the kidneys and livers of carp following induction. The study involved molecular analysis of the AMPs gene, followed by induction in carp. The experiment included four treatments: A (control), B (bacterial culture at 10⁸ CFU/mLat 15 mL/kg feed), C (5 mL/kg supernatant), and D (10 mL/kg supernatant), each with three replicates, where the treatments were mixed into the feed. Afterward, liver and kidney samples were analyzed for TLR2 gene expression. The results indicated the presence of surfactin and subtilin markers, with the detection of several AMPs genes, including SrfAA (surfactin) and SpaS (subtilin). The highest TLR2 gene expression in kidney and liver samples was observed in treatment B (addition of Bacillus CgM22 culture at 10⁸ CFU/mL at 15mL/ kg feed). These findings suggest that Bacillus CgM22 plays a role in modulating fish immunity by enhancing the body's defense mechanisms against pathogens. Overall, this study indicates that B. subtilisCgM22 has potential as a probiotic alternative to improve carp health through immune stimulation.