Comparative genomic and phenotypic analysis of potential beneficial properties of Bifidobacterium adolescentis

Certain strains of Bifidobacterium adolescentis inhabiting the gastrointestinal tract have been shown to possess properties that are purported to improve host health. However, given the genetic and phenotypic diversity that has been reported among B. adolescentis strains, it is unclear if and to what extent these traits are conserved across the species. Accordingly, we examined potentially beneficial properties using a combination of genomic and in vitro approaches. Phylogeny inferred from core genomes of 148 B. adolescentis isolates revealed five major lineages. At the functional genomic level, the strains were separated into three groups based on carbohydrate-active enzymes (CAZymes) that were predicted to act on a diverse range of substrates. Fifteen different B. adolescentis strains representing the major phylogenetic groups were tested in vitro for several metabolic traits. The ability to metabolize lactose (all strains; 2-232 β-galactosidase Miller units) and resistant starch (66% of strains; 26-74% utilization) and to produce γ-aminobutyric acid (80% of strains; 0.3-14.4 mM) and folate (all strains; 23-281 ng/mL) was common but showed substantial quantitative variation across strains under the conditions tested. Genes for the formation of antimicrobial compounds (7% of genomes) and antibiotic resistance (23% of genomes) were less frequent. While individual traits did not exhibit strong phylogenetic clustering, B. adolescentis strains had higher CAZyme gene counts relative to other comparison species, suggesting a broader adaptation for carbohydrate metabolism. Further studies on the distribution of beneficial traits and their genetic basis will provide insights into the contributions of B. adolescentis to health.IMPORTANCEBifidobacterium adolescentis is a gut commensal that is prevalent among healthy adults and centenarian populations, potentially contributing to host health through diverse functional properties. Here, through genomic and phenotypic analyses, we advanced our understanding of the prevalence of multiple potentially beneficial properties of B. adolescentis, including those associated with improving lactose tolerance, metabolic health, and mood, and supplying vitamins and inhibiting pathogens. Our findings revealed substantial quantitative variation in metabolic activities and production of relevant end-products across strains, highlighting the importance of strain-level differences and the health benefits they may confer. In addition, while the presence of specific genes was partially predictive of the magnitude of traits, the associations between genetics and phenotypes established here provide a foundation for improving future predictions.