The K26 capsular polysaccharide from Acinetobacter baumannii KZ-1098: Structure and cleavage by a specific phage...

Area of Science:

• Microbiology
• Carbohydrate Chemistry
• Genomics

Background:

• Acinetobacter baumannii produces diverse capsular polysaccharides (CPS) that contribute to its virulence and immune evasion.
• The KL26 gene cluster encodes for the K26 CPS, containing genes for unusual sugars like 6-deoxy-l-talose and D-mannose.

Purpose of the Study:

• To determine the precise chemical structure of the K26 capsular polysaccharide from Acinetobacter baumannii.
• To investigate the genetic basis and prevalence of the K26 CPS and its unique structural features.

Main Methods:

• Isolation and purification of K26 CPS from A. baumannii isolate KZ-1098.
• Structural elucidation using sugar analysis, Smith degradation, and comprehensive NMR spectroscopy (1D and 2D).
• Analysis of phage depolymerase activity and mass spectrometry for characterizing CPS fragments and linkages.

Main Results:

• The branched hexasaccharide repeating unit of K26 CPS was established, featuring a rare β-D-Manp-(1→2)-α-Manp linkage.
• A specific phage depolymerase (vB_AbaP_APK26) selectively cleaved this rare linkage.
• The genes responsible for this linkage (wzy_K26 and manC) are rare in A. baumannii genomes, found only in strains with KL26 or KL148 clusters.

Conclusions:

• The K26 CPS structure is fully elucidated, highlighting the presence of uncommon sugars and linkages in Acinetobacter baumannii.
• The genetic basis for the K26 CPS, including the rare D-mannose incorporation, is identified, with limited distribution in sequenced genomes.
• This research provides insights into the structural diversity and evolutionary pathways of Acinetobacter baumannii capsular polysaccharides.