Granulibacter bethesdensis can infect patients with
chronic granulomatous disease, an immunodeficiency caused by reduced phagocyte
NADPH oxidase function. Intact G. bethesdensis (Gb) is hypostimulatory compared to Escherichia coli, i.e.,
cytokine production in human blood requires 10-100 times more G. bethesdensis CFU/mL than E. coli. To better understand the pathogenicity of G. bethesdensis, we isolated its
lipopolysaccharide (GbLPS) and characterized its
lipid A. Unlike with typical Enterobacteriaceae, the release of presumptive Gb
lipid A from its LPS required a strong
acid. NMR and mass spectrometry demonstrated that the
carbohydrate portion of the isolated
glycolipid consists of α-Manp-(1→4)-β-GlcpN3N-(1→6)-α-GlcpN-(1⇿1)-α-GlcpA tetra-saccharide substituted with five acyl chains: the
amide-linked N-3' 14:0(3-
OH), N-2' 16:0(3-O16:0), and N-2 18:0(3-
OH) and the
ester-linked O-3 14:0(3-
OH) and 16:0. The identification of glycero-d-talo-oct-2-ulosonic
acid (Ko) as the first constituent of the core region of the LPS that is covalently attached to GlcpN3N of the
lipid backbone may account for the
acid resistance of GbLPS. In addition, the presence of Ko and only five acyl chains may explain the >10-fold lower proinflammatory potency of GbKo-lipidA compared to E. coli
lipid A, as measured by
cytokine induction in human blood. These unusual structural properties of the G.bethesdensis Ko-
lipid A glycolipid likely contribute to immune evasion during pathogenesis and resistance to
antimicrobial peptides.