Probiotic cell wall components as emerging postbiotics: structural diversity, immunoregulatory mechanisms, and health...

Probiotics exert health benefits through multifaceted interactions with the host, and accumulating evidence indicates that many of these effects are mediated by defined cell envelope-derived molecules rather than live bacteria per se. In parallel with the emerging concept of postbiotics, probiotic cell wall components, including peptidoglycan (PG), teichoic acids (TAs), exopolysaccharides (EPS), surface-layer proteins (SLPs), and bacterial extracellular vesicles (EVs), are increasingly recognized as key bioactive effectors that shape mucosal homeostasis. Herein, we summarize the major sources, preparation strategies, and structural features of these complex macromolecules, and highlight that their bioactivities are highly structure-dependent. Mechanistically, these components modulate probiotic adhesion and persistence, reinforce epithelial barrier integrity, interfere with pathogen colonization and biofilm formation, and regulate innate and adaptive immunity through pattern recognition receptors (PRRs). Furthermore, the emerging applications of probiotic cell wall components as postbiotic agents in functional foods and food additives, animal production, skin health, and pharmaceutical applications were further discussed. Understanding the intricate interplay between probiotic cell wall components and host immunity at the molecular level paves the way for innovative therapeutic and functional food developments.