Abstract
Bifidobacterium animalis subsp. lactis is a widely used probiotic, yet its efficacy is highly strain-specific, and growing antibiotic resistance necessitates rigorous safety evaluations. We used whole-genome sequencing and in vitro assays to characterize the safety and probiotic traits of infant feces-sourced strain BD1, which shows preliminary mood-modulating and anti-inflammatory potential. The BD1 genome showed a favorable safety profile. VFDB analysis identified 139 low-similarity homologs, with no major toxins detected. Only four chromosomally encoded antibiotic resistance genes were found; phenotypic testing confirmed resistance solely to tetracycline and mupirocin. Although the tetracycline resistance gene tet(W) was identified in genomic island GI01, the absence of associated mobile genetic elements results in a negligible risk of its mobilization. Functional annotation highlighted a dominant metabolic capacity for carbohydrate and amino acid metabolism. BD1 is rich in CAZymes, enabling superior utilization of diverse substrates (starch, sucrose, galactose). Enrichment in lipid metabolism pathways (glycerolipid, sphingolipid) further suggests potential for enhancing fermented product flavor. In vitro assessment demonstrated moderate gastrointestinal tolerance and strong bile salt tolerance. Surface properties showed pronounced cell surface hydrophobicity and confirmed biofilm-forming potential. In conclusion, BD1 exhibits robust safety, metabolic versatility, and strong probiotic characteristics, supporting its development as a functional probiotic strain.