Insights into endogenous Bifidobacterium species in the human gut microbiota during adulthood

Bifidobacteria are among the earliest and most abundant bacterial colonizers of the neonatal gut in many mammals, where they elicit purported host health benefits. While early life-associated dynamics and diversity, as well as the metabolic and beneficial activities, of Bifidobacterium species have been well studied, functional contributions of bifidobacteria to health and well-being of adults remain less explored. In this opinion piece, we discuss the current knowledge regarding the relevance of endogenous Bifidobacterium species associated with adulthood. We identify knowledge gaps and discuss opportunities for microbiota enrichment with rationally selected strains of Bifidobacterium more adapted to the adult host. We propose that current knowledge and future studies in this area will help us to better understand the ecological, metabolic, and functional roles played by Bifidobacterium in the gut ecosystem across various host ages.