K units of the K8 and K54 capsular polysaccharides produced by Acinetobacter baumannii BAL 097 and RCH52 have the same structure but contain different di-N-acyl derivatives of legionaminic acid and are linked differently

The K8 and K54 capsular polysaccharides were isolated from Acinetobacter baumannii BAL 097 and RCH52, respectively, and studied by sugar analysis, partial acid hydrolysis and selective solvolysis with CF₃CO₂H in the presence of 2-methyl-1-propanol, along with 1D and 2D ¹H and ¹³C NMR spectroscopy. The following structures of related branched tetrasaccharide repeats (K units) of the polysaccharides were established:[Figure presented] where Leg indicates 5,7-diamino-3,5,7,9-tetradeoxy-D-glycero-D-galacto-non-2-ulosonic (legionaminic) acid and R indicates (R)-3-hydroxybutanoyl or acetyl in the ratio ~2.5:1. The sequences of the KL8 and KL54 capsule gene clusters were closely related. The difference in the acyl group at O-7 on the sidechain legionaminic acid is due to differences in two genes in the legionaminic acid biosynthesis cluster. The wzy genes encoding the K unit polymerases are also different and make different linkages between the K units, allowing the first sugar of both K units to be identified as D-GlcpNAc. The shared Gtr20 glycosyltransferase, also encoded in KL63, forms the α-L-FucpNAc-(1 → 3)-D-GlcpNAc linkage, and Gtr19 was predicted to form α-D-GalpNAc-(1 → 3)-L-FucpNAc. Gtr18 from KL8 is 75% identical to Gtr108 from KL54 and both would link the Leg derivative to D-GalpNAc. Hence the genes present at the K locus were consistent with the composition and structures of the K8 and K54 capsular polysaccharides.