A novel esterase regulates Klebsiella pneumoniae hypermucoviscosity and virulence
Klebsiella pneumoniae , an emerging multidrug-resistant pathogen, exhibits hypermucoviscosity (HMV) as a critical virulence trait mediated by its capsular polysaccharide (CPS). Recent discoveries have determined acetylation as a significant modification for CPS, although its impact on HMV and virulence was previously unknown. This study elucidates the roles of two enzymes: K lebsiella p neumoniae A cetylated C PS E sterase (KpACE), an esterase that removes acetyl groups from CPS, and WcsU, an acetyltransferase that adds acetyl groups to CPS. KpACE is highly upregulated in an ompR -deficient mutant lacking HMV, and its overexpression consistently reduces HMV and diminishes virulence in a mouse model of pneumonia. The esterase domain-containing KpACE effectively deacetylates model sugar substrates and CPS-K2. Site-directed mutagenesis of the conserved catalytic histidine residue at position 370 significantly reduces its enzymatic activity. This reduction correlates with decreased HMV, affecting key virulence traits including biofilm formation and serum resistance. Similarly, a deficiency in the wcsU gene abolishes CPS acetylation, and reduces HMV and virulence. These results highlight the importance of the delicate balance between CPS acetylation by WcsU and deacetylation by KpACE in regulating the pathogenicity of K . pneumoniae . Understanding this balance provides new insights into the modulation of virulence traits and potential therapeutic targets for combating K . pneumoniae infections. Klebsiella pneumoniae is an antibiotic-resistant pathogen known for its virulence factor, hypermucoviscosity (HMV), which relies on the production of capsular polysaccharides (CPS). This study highlights the roles of two key enzymes: KpACE, an esterase that removes acetyl groups from CPS, and WcsU, an acetyltransferase that adds acetyl groups to CPS. Overexpression of KpACE reduces HMV and decreases virulence in a mouse pneumonia model by deacetylating CPS. Conversely, a deficiency in the wcsU gene, which is responsible for acetylating CPS, also results in decreased HMV and virulence. The balance between CPS acetylation by WcsU and deacetylation by KpACE is crucial in regulating K . pneumoniae pathogenicity. This balance affects various virulence factors, including biofilm formation and serum resistance, highlighting the importance of CPS acetylation dynamics in the pathogen’s fitness and virulence. Understanding these mechanisms offers insights into potential therapeutic targets to mitigate the virulence and antibiotic resistance of K . pneumoniae .
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