The phosphate groups of lipopolysaccharides increase the overall negative charge of the cell membrane and help to stabilize the structure. The inner core glycan residues are typically phosphorylated or modified with phosphate-containing groups, e.g., pyrophosphate or 2‑aminoethylphosphate. The KDO-containing inner core also is modified with heptulose (ketoheptose) monosaccharides, the most common of which is L-glycero-α-D-manno-heptopyranose. 2 However, an Escherichia coli K-12 suppressor strain that is KDO deficient demonstrates that the KDO requirement is not absolute for viability. KDO is specifically associated with lipopolysaccharide, and biologically active lipid A was thought to require at least one KDO residue for bacterial survival. The inner polysaccharide core typically contains between 1 and 4 molecules of the KDO (3‑deoxy-α-D-manno-octulosonic acid) attached to the disaccharide core. The acyl chain length and number of acyl groups may vary between bacterial species but are relatively conserved within a species. The lipid A core is made up of a β-glucosamine-(1→6)-glucosamine-1-phosphate base with fatty acid esters attached to both carbohydrates.