Bifidobacterium as Keystone Species Driving Microbial Interactions in the Infant Digestive Tract

<i>Bifidobacterium</i> plays a keystone role in the ecological assembly of the infant-gut microbiome and in shaping host immune and metabolic development. These anaerobic bacteria possess specialized transporters and glycosyl hydrolases that enable the degradation of human milk oligosaccharides (HMOs), driving early microbial succession through coexistence, competition, and priority effects. Their fermentation products, mainly acetate and lactate, acidify the gut environment, inhibit pathogens, and sustain cross-feeding with butyrate-producing microbes, whereas aromatic lactic acids contribute to immune modulation. Ecological and clinical evidence indicates that loss of <i>Bifidobacterium</i> perturbs community structure and increases disease risk. Understanding these interactions has guided the design of HMO-based and synbiotic strategies that aim to restore healthy colonization patterns. Ongoing efforts now integrate ecological, metabolic, and computational approaches to better predict and replicate the health-promoting functions of <i>Bifidobacterium</i> throughout life.