Fig. 1. Schematic representation of the Gram-negative cell envelope and LPS structure. The Gram-negative cell envelope consists of three primary layers (left). The inner membrane is a symmetric glycerophospholipid bilayer that is separated from the outer membrane by a thin layer of peptidoglycan-based cell wall located in the periplasm. The outer membrane is an asymmetric bilayer with glycerophospholipids in the inner leaflet and primarily LPS in the outer leaflet. The single magnified LPS molecule (right) is made up of lipid A, a non-repeating core oligosaccharide, and the O-antigen domain comprised of a repeating polymer of variable lengths, represented by (n). Lipid A is a disaccharide of glucosamine that is both fatty acylated and phosphorylated. The hexa-acylated bis-phosphorylated lipid A structure of E. coli is shown. Created in part using BioRender.com.