Re-investigation of the structure of the capsular polysaccharide of Klebsiella K15 using bacteriophage degradation and inverse-detected NMR experiments

Exploring the enzymatic activity of depolymerase gp531 from Klebsiella pneumoniae jumbo phage RaK2

Klebsiella pneumoniae poses a major global challenge due to its virulence, multidrug resistance, and nosocomial nature. Thus, bacteriophage-derived proteins are extensively being investigated as a means to combat this bacterium. In this study, we explored the enzymatic specificity of depolymerase gp531, encoded by the jumbo bacteriophage vB_KleM_RaK2 (RaK2). We used two different methods to modify the reducing end of the oligosaccharides released during capsule hydrolysis with gp531. Subsequent acidic cleavage with TFA, followed by TLC and HPLC-MS analyses, revealed that RaK2 gp531 is a β-(1→4)-endoglucosidase. The enzyme specifically recognizes and cleaves the capsular polysaccharide (CPS) of the Klebsiella pneumoniae K54 serotype, releasing K-unit monomers (the main product), dimers, and trimers. Depolymerase gp531 remains active from 10 to 50 °C and in the pH 3-8 range, indicating its stability and versatility. Additionally, we demonstrated that gp531's activity is not affected by CPS acetylation, which is influenced by the growth conditions of the bacterial culture. Overall, our findings provide valuable insights into the enzymatic activity of the first characterized depolymerase targeting the capsule of the clinically relevant K54 serotype of K. pneumoniae.

Capsular types of Klebsiella pneumoniae revisited by wzc sequencing

Capsule is an important virulence factor in bacteria. A total of 78 capsular types have been identified in Klebsiella pneumoniae. However, there are limitations in current typing methods. We report here the development of a new genotyping method based on amplification of the variable regions of the wzc gene. Fragments corresponding to the variable region of wzc were amplified and sequenced from 76 documented capsular types of reference or clinical strains. The remaining two capsular types (reference strains K15 and K50) lacked amplifiable wzc genes and were proven to be acapsular. Strains with the same capsular type exhibited ≧94% DNA sequence identity across the variable region (CD1-VR2-CD2) of wzc. Strains with distinct K types exhibited <80% DNA sequence identity across this region, with the exception of three pairs of strains: K22/K37, K9/K45, and K52/K79. Strains K22 and K37 shared identical capsular polysaccharide synthesis (cps) genes except for one gene with a difference at a single base which resulted in frameshift mutation. The wzc sequences of K9 and K45 exhibited high DNA sequence similarity but possessed different genes in their cps clusters. K52 and K79 exhibited 89% wzc DNA sequence identity but were readily distinguished from each other at the DNA level; in contrast, strains with the same capsular type as K52 exhibited 100% wzc sequence identity. A total of 29 strains from patients with bacteremia were typed by the wzc system. wzc DNA sequences confirmed the documented capsular type for twenty-eight of these clinical isolates; the remaining strain likely represents a new capsular type. Thus, the wzc genotyping system is a simple and useful method for capsular typing of K. pneumoniae.

Klebsiella K43 capsular polysaccharide: primary structure and depolymerisation by a viral-borne endoglycanase

The capsular polysaccharide of Klebsiella K43 has been studied by glycose analysis, methylation analysis, and NMR spectroscopy, and by bacteriophage depolymerisation of the native polysaccharide. Additional evidence for the structure of the repeating unit came from base-catalysed degradation of the methylated polysaccharide, and from NMR spectroscopic analysis of the lithium-degraded polysaccharide and of the oligosaccharide-alditol derived from the repeating unit oligosaccharide obtained from a bacteriophage degradation. The polysaccharide was shown to have the repeating unit: [formula: see text]