Figure 1.

Cell envelope of the Gram-negative bacteria is composed of two layers of lipid bilayer membranes and an aqueous periplasmic space sandwiched in between. The outer membrane (OM) is an asymmetric bilayer with lipopolysaccharide (LPS) on the outer leaflet and phospholipids on the inner leaflet. Porins on the OM aid passive diffusion of nutrients and antibiotics. The inner membrane (IM) is composed of phospholipids and contains transporters. A thin layer of peptidoglycan (PG) cell wall exists in the periplasm, which is anchored to the outer membrane by Bruan’s lipoprotein (Lpp). The periplasm is also rich in macromolecules including proteins and glycans. OPGs are special glucans with a glucose backbone and modifications such as phosphoethanolamine, phosphoglycerol, and succinyl residues. OPGs contribute to the net negative potential across the OM. The selective permeability of the outer membrane leads to the development of a membrane potential. The figure was created using BioRender.com.