Acinetobacter baumannii k106 and k112: Two structurally and genetically related 6-deoxy-l-talose-containing capsular polysaccharides

Whole genome sequences of two Acinetobacter baumannii clinical isolates, 48-1789 and MAR24, revealed that they carry the KL106 and KL112 capsular polysaccharide (CPS) biosynthesis gene clusters, respectively, at the chromosomal K locus. The KL106 and KL112 gene clusters are related to the previously described KL11 and KL83 gene clusters, sharing genes for the synthesis of L-rhamnose (L-Rhap) and 6-deoxy-L-talose (L-6dTalp). CPS material isolated from 48-1789 and MAR24 was studied by sugar analysis and Smith degradation along with one-and two-dimensional 1H and 13C NMR spectroscopy. The structures of K106 and K112 oligosaccharide repeats (K units) L-6dTalp-(1→3)-D-GlcpNAc tetrasaccharide fragment share the responsible genes in the respective gene clusters. The K106 and K83 CPSs also have the same linkage between K units. The KL112 cluster includes an additional glycosyltransferase gene, Gtr183, and the K112 unit includes α L-Rhap side chain that is not found in the K106 structure. K112 further differs in the linkage between K units formed by the Wzy polymerase, and a different wzy gene is found in KL112. However, though both KL106 and KL112 share the atr8 acetyltransferase gene with KL83, only K83 is acetylated.