Research letterChemical structure of the lipid A component of Plesiomonas shigelloides and its taxonomical significance

The chemical structure of the lipid A moiety of the lipopolysaccharide of the type strain of Plesiomonas shigelloides was elucidated. It consists of a β-(1 → 6)-linked glucosamine disaccharide carrying phosphate groups at C-1 of the reducing and at C-4′ of the non-reducing glucosamine. It contains a total of 6 residues of fatty acids, 2 amide-linked and 4 ester-linked. The amino groups of the backbone disaccharide are N-acylated by substituted 3-hydroxyacyl residues: at the reducing glucosamine by 3-O-(14:0)14:0; and at the non-reducing glucosamine by 3-O-(12:0)14:0. Two residues of 3-hydroxytetradecanoic acid are linked to C-3 and C-3′ of the glucosamine residues; the hydroxy groups of these ester-linked 3-hydroxytetradecanoic acids are unsubstituted. In free lipid A, the hydroxyl groups at C-4 and C-6′ are unsubstituted, indicating that the 2-keto-3-deoxyoctonic acid (KDO) is linked to C-6′ of the non-reducing glucosamine, as was shown with enterobacterial lipid A. The taxonomical significance of these structural details is discussed.