Global biogeography of Bifidobacterium infantis: stratification and precision probiotic design.

Bifidobacterium longum and B. infantis are recognized as pivotal pioneer colonizers in the infant gut, playing instrumental roles in supporting growth, immune maturation, and pathogen resistance. Despite their significance, current genomic understanding is heavily biased toward a limited pool of historical isolates from high-income countries (HICs), leaving the natural diversity of strains circulating in low- and middle-income countries (LMICs) largely uncharted. To address this gap, Shao et al. constructed an unprecedented global genomic atlas comprising 4098 high-quality genomes from 48 countries, thereby expanding LMIC representation by 12- to 17-fold. Through high-resolution phylogenomic and functional analyses, the authors not only delineated B. infantis and B. longum as distinct species with divergent evolutionary histories but also uncovered profound biogeographic stratification and diet-driven metabolic adaptations at the strain level. These findings challenge the suitability of current probiotic strains and establish a robust scientific blueprint for developing next-generation, geographically matched therapeutics tailored to diverse infant populations.