Phenotypic, secondary metabolite, and genomic characterization of Bacillus siamensis B03 from brackish water with Anti‑Vibrio potential

Abstract

This study aimed to provide the first genomic, functional, and metabolic characterization of Bacillus siamensis B03 from Lang Co Bay, Vietnam, and to evaluate the hypothesis that it harbors unique metabolic traits and antimicrobial potential against Vibrio spp.. B03 showed no hemolytic activity, moderate biofilm formation, tolerance to 10% NaCl, and broad extracellular enzyme secretion. Ethyl acetate extracts from the cell-free supernatant exhibited in vitro antibacterial activity against five Vibrio species, with inhibition zones of 14.7–22.3 mm. Metabolomic analysis tentatively identified 20 compounds, mainly cyclic dipeptides, some previously reported to possess antimicrobial properties. Draft, plasmid-free genome (3,745,205 bp; 46.4% GC) encodes 3,561 proteins and 72 tRNAs, with genes mainly for amino acid and carbohydrate metabolism, and contains gene clusters for bacillaene, fengycin, difficidin, bacillibactin (100% similarity), and surfactin (78%). Pan-genome analysis of 24 B. siamensis genomes revealed 2,254 core genes, with B03 contributing 31 unique genes, including those encoding NAD-dependent malic enzyme and adenylation domain proteins. These findings suggest B. siamensis B03 as a potential control agent against Vibrio pathogens.