Structure of the K128 capsular polysaccharide produced by Acinetobacter baumannii KZ-1093 from Kazakhstan

The structure of the K128 capsular polysaccharide (CPS) produced by Acinetobacter baumannii isolate KZ-1093 from Kazakhstan was established by sugar analysis and Smith degradation along with 1D and 2D ¹H and ¹³C NMR spectroscopy. The CPS was found to consist of branched pentasaccharide repeating units containing only neutral sugars, and its composition and topology are closely related to those of the A. baumannii K116 CPS. The K128 and K116 oligosaccharide units differ in the linkage between the disaccharide side chain and the main chain, with a β-(1 → 6) linkage in K128 replacing a β-(1 → 4) linkage in K116. The linkages between the repeating units in the K128 and K116 CPSs are also different, with K128 units linked by β-d-GalpNAc-(1 → 4)-d-Galp, and β-d-GalpNAc-(1 → 3)-d-Galp linkages between K116 units. The KZ-1093 genome was sequenced and the CPS biosynthesis gene cluster at the chromosomal K locus was designated KL128. Consistent with the CPS structures, KL128 differs from KL116 in one glycosyltransferase gene and the gene for the Wzy polymerase. In KL128, the gtr200 glycosyltransferase gene replaces gtr76 in KL116, and Gtr200 was therefore assigned to the different β-d-GalpNAc-(1 → 6)-d-Galp linkage in K128. Similarly, the Wzy_K128 polymerase could be assigned to the β-d-GalpNAc-(1 → 4)-d-Galp linkage between the K128 units.