Evaluation of Effects and Genomic Analysis of Aquaculture Probiotic Strains With Antioxidant and Enzymatic Activity

During a screening for potential probiotics for aquaculture, several Bacillus strains with enzymatic and antioxidant activity were isolated. Following cross-antagonistic activity assays, two pairs of strains were prioritized: Bacillus velezensis MT14 and MT42, which displayed both proteolytic and amylolytic functions, and Bacillus subtilis MT48 and MT74, which additionally demonstrated antioxidant capacity. Potential probiotic strains were introduced into starter feeds for sterlet larvae for 2 months. Both experimental groups demonstrated weight gain compared to the control. The proportion of fish with higher weight increased by 9.65% in Group 1 and by 14.75% in Group 2. A reduction in IL-1β gene expression occurred in both groups, suggesting a reduction in inflammation. Group 2 exhibited decreased expression of IGF-1, HSP 70, and GST genes, which may indicate a positive impact of the antioxidant activity of the potential probiotic on alleviating stress. Genomic sequencing revealed that only the strains with antioxidant activity possessed genes coding pulcherriminic acid, bacillibactin, subtilosin, and fengicin synthetases-a feature absent in other strains. This finding implies that these metabolites, especially pulcherriminic acid, may contribute to the antioxidant properties of these strains. These results highlight the importance of considering strain-specific characteristics when developing probiotics tailored to the requirements of aquaculture.