Genomic insights into the probiotic potential of Bacillus velezensis D-18 for aquaculture

The identification of safe and functionally robust probiotics is a key challenge for sustainable aquaculture and requires genome-based validation of candidate strains. Here, we performed an integrative genomic characterization of Bacillus velezensis D-18, a strain previously shown to enhance disease resistance in European seabass. Whole-genome sequencing generated a draft genome of approximately 4.06 Mb containing 4,178 protein-coding genes and 84 RNA genes. Comparative genomics confirmed the taxonomic placement of the strain within the B. velezensis lineage and its clear separation from pathogenic members of the Bacillus cereus group. Genome-wide screening detected no acquired antimicrobial resistance genes or virulence determinants, supporting the biosafety of the strain. Functional annotation revealed genetic determinants associated with quorum quenching, biofilm formation, stress tolerance, and antimicrobial activity. AntiSMASH analysis further identified seven biosynthetic gene clusters encoding bioactive metabolites including surfactin, fengycin, bacilysin, and macrolactin. In addition, molecular docking analyses suggested potential interactions between bacterial proteins and mucin glycoproteins, consistent with previously reported mucus adhesion. Together, these findings provide a genomic framework supporting the probiotic potential of B. velezensis D-18 for aquaculture applications.