In Vitro Evaluation of Halotolerant Bacillus velezensis 24.5 as a Promising Probiotic with Broad-Spectrum Antimicrobial Activity

The remarkable metabolic adaptability of Bacillus velezensis, including efficient nutrient use, spore formation, and the secretion of antimicrobial peptides, supports its expanding role in biotechnological applications ranging from crop protection to probiotic development. In this study, the halotolerant strain 24.5 was identified as B. velezensis through 16S rDNA and gyrA gene sequencing. PCR analyses confirmed the presence of genes responsible for polyketides, lipopeptides, and dipeptides biosynthesis. These results indicate the potential for the production of structurally diverse bioactive metabolites. Strain 24.5 demonstrated remarkable antimicrobial activity against 19 bacterial pathogens and three Candida species (p < 0.05). The study demonstrated high survival rates under simulated gastrointestinal conditions, suggesting strong adaptability for gut colonization. Antioxidant evaluation revealed DPPH radical scavenging activities of 34.68% for intact cells and 18.47% for the cell-free extract (p < 0.05). The enzymatic profile highlighted versatile metabolic functions, supporting its multifaceted probiotic potential. Auto-aggregation reached 84.42% at 24 h, and high hydrophobicity toward hexane (71.62%) supported adhesion potential. Antibiotic susceptibility profiling showed sensitivity or intermediate susceptibility to 22 of 24 tested antibiotics (p < 0.05). No haemolytic activity was detected, supporting its safety profile. Overall, these results emphasise the adaptability and multifunctional properties of Bacillus velezensis strain 24.5, highlighting its potential as a promising probiotic candidate for applications in food safety and biotechnology.