Isolation, characterization of Bacillus subtilis and Bacillus amyloliquefaciens and validation of the potential probiotic efficacy on growth, immunity, and gut microbiota in hybrid sturgeon (Acipenser baerii ♀ × Acipenser schrenckii ♂).

Probiotics are increasingly considered as an alternative to antibiotics in developing environmentally sustainable aquaculture practices. Hybrid sturgeon (Acipenser baerii ♀ × Acipenser schrenckii ♂), a globally popular species valued for its nutritional content and caviar, has limited research on host-associated probiotics. In this study, we isolated and identified Bacillus subtilis and Bacillus amyloliquefaciens from healthy hybrid sturgeon and assessed their impact on growth, immunity, gut microbiota, and transcriptome following an 8-week feeding trial. The isolated strains demonstrated strong production of protease, amylase, lipase, and cellulase, along with broad-spectrum pathogen inhibition, including Aeromonas veronii, Aeromonas sobria, and Yersinia ruckeri. Supplementation with B. subtilis and B. amyloliquefaciens significantly improved growth performance and increased survival rates against A. veronii infection. Mechanistically, probiotics altered gut microbiota composition, enhancing digestive functions. Transcriptome analysis further revealed that probiotic supplementation boosted immune response and protein digestion and absorption. These findings suggest that B. subtilis and B. amyloliquefaciens are promising probiotic candidates for the hybrid sturgeon industry, offering effective protection against A. veronii infection.