Taxonomic and functional remodeling of the gut microbiota during aging and implications for microbiota-derived biomarkers.

The gut microbiota represents a complex microbial ecosystem that contributes to host metabolic regulation, immune homeostasis, and intestinal barrier function. Across the lifespan, gut microbial communities exhibit marked taxonomic and functional variation driven by environmental exposures, dietary patterns, medication use, and age-associated immune alterations. These differences are closely linked to chronic inflammatory states and immune dysregulation that accompany aging. This review synthesizes current evidence on age-associated differences in gut microbiota composition and functional capacity, with a focus on microbial traits and metabolic pathways relevant to host-microbe interactions. Pathological aging is frequently associated with reduced microbial diversity, loss of short-chain fatty acid-producing commensal bacteria, and enrichment of opportunistic or pro-inflammatory taxa. In contrast, healthy aging and longevity are commonly associated with more stable, resilient, and metabolically adaptable microbial communities. At the functional level, recurrent alterations in short-chain fatty acid biosynthesis, bile acid transformation, and tryptophan- and choline-related metabolic pathways define conserved features across aging-associated microbial profiles. Across neurodegenerative, metabolic, and cardiovascular conditions, overlapping taxonomic and functional patterns indicate shared microbiota-associated signatures linked to inflammatory states. Advances in metagenomic sequencing, functional annotation, and microbiome-focused biotechnological approaches now enable integrated analysis of microbial structure and metabolic potential. These developments provide a robust framework for identifying reproducible microbiome-based indicators relevant to aging-associated physiological changes and for translating microbiome research into biotechnology-driven applications.