Capsular Polysaccharide of Acinetobacter baumannii MRSN 31196 (a KL1 Variant Strain) and its Degradation by a Recombinant Depolymerase from Bacteriophage vB_AbaP_B5.

Acinetobacter baumannii MRSN 31196 was assigned as KL1, but has now been reassigned as KL1-v as new polymerase wzy and acetyl transferase (atr25) genes are discovered outside of its gene locus due to horizontal gene transfer. Its capsular polysaccharide (CPS), namely K1v, was isolated by a standard water-phenol extraction and an aqueous base extraction. K1v is degradable by a recombinant phage depolymerase B5 which is known to hydrolyze A. baumannii K9 CPS. The structure of oligosaccharides obtained were determined by NMR and mass spectroscopic analysis. The results showed that the K1v structure is closely related to K1 CPS, with the same sugar composition and linkages except β-QuiNAcNR-(1-3)-GlcNAc in K1v replaced β-QuiNAcNR-(1-4)-GlcNAc in K1, due to an altered Wzy. However, the atr25 gene is likely silenced, or the transferase activity is inhibited, as K1v is not O-acetylated. We also found that the N-acetyl and N-3-hydroxybutyryl (HBu) substitutions (R) in QuiNAcNR has approximately a 1:1 ratio. The mass spectroscopic analysis provided evidence that structural blocks with consecutive QuiNAcNAc or QuiNAcNHBu are present in the polysaccharide. The K1v CPS structure has the following trisaccharide repeating unit.