Figure 1. This figure depicts cell wall envelope of the Gram-negative bacteria and biogenesis of Outer membrane vesicles (OMV). Gram-negative bacteria consists of two membrane. Outer leaflet of the outer membrane (OM) is composed of lipopolysaccharide (LPS). To stabilize membrane integrity, Braun's lipoprotein in the OM crosslinks OM layer and peptidoglycan (PG). Also Outer membrane protein A non-covalently binds with PG layer. The Tol-Pal complex which is consisted with cytoplasmic proteins, periplasmic protein, and outer membrane lipoprotein (peptidoglycan-associated lipoprotein) binds cell wall envelope together. OMV is generated from the OM by several mechanisms including reducing cell wall envelope crosslinks, LPS remodeling, and bilayer couple model by increasing OM fluidity. Periplasmic proteins including various virulence factors and cellular waste such as misfolded proteins are packaged into OMVs as cargos and secreted.