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Capsular Polysaccharide of Acinetobacter baumannii MRSN 31196 (a KL1 Variant Strain) and its Degradation by a
Evguenii Vinogradov1, Lillian Zou2, Jacek Stupak1
1Human Health Therapeutic Research Center, National Research Council Canada, 100 Sussex Drive, Ottawa, Ontario, Canada, K1A 0R6.
Abstract:
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.
Insights
Acinetobacter baumannii strain MRSN 31196
Area of Science:
- Microbiology
- Structural Biology
- Genetics
Background:
- Acinetobacter baumannii is an opportunistic pathogen.
- Capsular polysaccharide (CPS) structures are crucial for A. baumannii virulence.
- Strain MRSN 31196 was previously classified as KL1.
Purpose of the Study:
- To re-evaluate the classification of A. baumannii MRSN 31196.
- To elucidate the structure of its capsular polysaccharide (CPS).
- To investigate the genetic basis of CPS biosynthesis.
Main Methods:
- Horizontal gene transfer analysis.
- Capsular polysaccharide (CPS) isolation using water-phenol and aqueous base extraction.
- Structural elucidation via NMR and mass spectrometry.
- Phage depolymerase activity assay.
Main Results:
- Strain MRSN 31196 is reclassified as KL1-v due to novel polymerase (wzy) and acetyl transferase (atr25) genes.
- The K1v CPS structure is similar to K1 CPS but with a distinct linkage (β-QuiNAcNR-(1-3)-GlcNAc).
- The atr25 gene appears silenced, as K1v is not O-acetylated.
- A 1:1 ratio of N-acetyl and N-3-hydroxybutyryl (HBu) substitutions was observed.
Conclusions:
- The reassignment of A. baumannii MRSN 31196 to KL1-v is supported by genetic and structural data.
- The K1v CPS structure exhibits unique characteristics compared to K1 CPS.
- Horizontal gene transfer plays a role in the evolution of A. baumannii CPS diversity.
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