Safety and amino acid profiles of Bacillus safensis in soybean fermentation

This study evaluated the antibiotic resistance, toxigenic potential, and amino acid (AA) production profiles of four Bacillus safensis strains in soybean fermentation. Minimum inhibitory concentration tests revealed intrinsic resistance to chloramphenicol and clindamycin, supported by the chromosomal presence of the catA gene. No other acquired resistance genes were identified. Virulence genes associated with foodborne illness in Bacillus cereus-including nhe, hbl, cytK, and ces-were not detected in any strain, confirming the absence of typical toxin-associated determinants. Analysis of free AAs revealed that all B. safensis strains significantly increased levels of 15 proteinogenic AAs, including all nine essential AAs, in soybean cultures. Principal component analysis of 22 AAs demonstrated that B. safensis strains, especially KGU003, induced characteristic increases in alanine, glutamic acid, glutamine, and γ-aminobutyric acid (GABA). Notably, three of the four strains produced higher levels of GABA than Bacillus velezensis DMB06, a known high GABA producer, with KGU003 generating over 3-fold more. These results indicate that B. safensis strains meet core safety criteria and possess distinctive AA production profiles. Therefore, B. safensis represents a strong candidate as a safe and functional starter culture for developing fermented soybean foods with enhanced nutritional and functional properties.