Structure and gene cluster of the K93 capsular polysaccharide of Acinetobacter baumannii B11911 containing 5-N-Acetyl-7-N-[(R)-3-hydroxybutanoyl]pseudaminic acid

Capsular polysaccharide (CPS) assigned to the K93 type was isolated from the bacterium Acinetobacter baumannii B11911 and studied by sugar analysis along with oneand two-dimensional 1 H and 13 C NMR spectroscopy. The CPS was found to contain a derivative of pseudaminic acid, and the structure of the branched tetrasaccharide repeating unit was established. Genes in the KL93 capsule biosynthesis locus were annotated and found to be consistent with the CPS structure established. The K93 CPS has the α-D-Gal p -(1→6)-β-D-Gal p -(1→3)-D-Gal p NAc trisaccharide fragment in common with the K14 CPS of Acinetobacter nosocomialis LUH 5541 and A. baumannii D46. It also shares the β-D-Gal p -(1→3)-DGal p NAc disaccharide fragment and the corresponding predicted Gal transferase Gtr5, as well as the initiating GalNAc-1P transferase ItrA2, with a number of A. baumannii strains.