Structure of Klebsiella grimontii K15g Capsular Polysaccharide and Products of Its Cleavage by Phage Silvester Depolymerase

Abstract Klebsiella grimontii is a recently described pathogen (former member of the Klebsiella oxytoca phylogroup K06), which has been elevated to the rank of a new species. The capsular polysaccharide (CPS) of K. grimontii is a principal virulence factor that significantly enhances the capacity of the bacterium to induce infections. The structure of CPS from K. grimontii strain K15g determined is this study was found to represent a novel type of polysaccharide consisting of branched hexasaccharide K-units, each composed of four monosaccharides of the main chain and a disaccharide side chain containing pyruvic acid 4,6-acetal residues. Since the CPS cleavage initiates the infection of bacterial cells by a phage, we investigated the depolymerase activity of the phage Silvester structural protein and demonstrated that the recombinant depolymerase of the phage Silvester cleaved K. grimontii K15g CPS at the β-D-GlcpA-(1→2)-α-L-Rhap linkage between the repeating units. The pathway for the synthesis of CPS of this type was proposed. Graphical abstract