New insights into outer membrane vesicles in Gram-negative bacteria from biogenesis to applications.

Nano-sized outer membrane vesicles (OMVs) are lipid-bilayered structures that primarily encapsulate periplasmic components, with minor inclusion of cytoplasmic materials. Rather than passive byproducts of cellular damage, OMVs are now understood as active mediators of bacterial physiology, environmental adaptation, and host interaction. Recent evidence identifies envelope instability as a key mechanistic driver of OMV biogenesis. Disruptions in outer membrane-peptidoglycan connectivity, imbalances in periplasmic homeostasis, and alterations in lipid asymmetry collectively promote vesicle formation as a regulated adaptive response. Under stress conditions, OMVs acquire specialized functional roles, selectively enriching specific cargo and exhibiting surface properties that enable them to sequester host-derived antimicrobial factors. OMV-associated biomolecules further influence vesicle uptake into host cells through distinct endocytic pathways, shaping intracellular trafficking and downstream functional outcomes. Following internalization, pathogen-derived OMVs disrupt host signaling pathways and are exploited to promote immune evasion, whereas commensal-derived OMVs contribute to microbiota homeostasis and immune modulation. In parallel, growing efforts to harness OMVs as vaccine platforms highlight their potential as innovative tools for both therapeutic and prophylactic applications. Collectively, these insights position OMVs as critical mediators of bacterial pathogenicity and as promising targets for anti-infective strategies.