Phage depolymerase modulates virulence and biofilm in hypervirulent Klebsiella pneumoniae: a trade-off between capsular polysaccharide and type 3 fimbriae

Capsular polysaccharides (CPS) and type 3 fimbriae are key virulence factors in hypervirulent Klebsiella pneumoniae (hvKp); however, their potential interactions remain inadequately understood. In this study, we isolated a K2-type hvKp strain, A25, which exhibited weak biofilm formation. Additionally, we identified a novel depolymerase, Dpo11, capable of specifically degrading the K2-type CPS. Upon treatment with Dpo11, strain A25 showed reduced virulence while exhibiting enhanced biofilm formation. Further studies revealed that CPS inhibits biofilm formation by downregulating the expression of the type 3 fimbriae operon mrkABCDF. And in vivo experiments demonstrated that CPS significantly suppresses the virulence of type 3 fimbriae. Meanwhie, we found that the inhibitory effect of CPS on biofilm formation is widely present in hvKp strains. These results demonstrated a trade-off relationship between the virulence factors CPS and type 3 fimbriae. When CPS is present, biofilm and virulence mediated by type 3 fimbriae are suppressed. In contrast, when CPS is absent, type 3 fimbriae become a more critical virulence factor, promoting biofilm formation and potentially facilitating chronic infection. In summary, our findings revealed a complex interplay between CPS and type 3 fimbriae, providing deeper insights into the pathogenicity of hvKp.