Structure of the K6 capsular polysaccharide from Acinetobacter baumannii isolate RBH4

• Capsule structure was obtained for Acinetobacter baumannii clinical isolate RBH4.
• Capsule repeating unit is linear and consists of four monosaccharide residues.
• Third case of 5,7-di-N-acetylpseudaminic acid as component of Acinetobacter capsule.
• Glycosyltransferases and the Wzy polymerase were assigned to the formation of glycosidic bonds.

The structure of the capsular polysaccharide (CPS) from an Acinetobacter baumannii global clone 2 (GC2) clinical isolate RBH4 that carries the KL6 gene cluster was elucidated by means of chemical and spectroscopical methods. The repeating unit of K6 CPS is linear and contains N-acetyl-d-galactosamine (d-GalpNAc), two d-galactose (d-Galp) residues and 5,7-di-N-acetylpseudaminic acid (Pse5Ac7Ac). The synthesis of these sugars could be attributed to genes in the KL6 capsule biosynthesis gene cluster, and the formation of the linkages between the sugars were assigned to glycosyltransferases or the Wzy polymerase encoded in KL6.

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