Abstract

Klebsiella pneumoniae CG43, a heavy encapsulated liver abscess isolate, mainly expresses type 3 fimbriae. Type 1 fimbriae expression was only apparent in CG43S3ΔmrkA (the type 3 fimbriae-deficient strain). The expression of type 1 fimbriae in CG43S3ΔmrkA was reduced by deleting the fimK gene, but was unaffected by removing the 3'end of fimK encoding the C-termial EIL domain (EIL_fimK). Quantitative reverse-transcription PCR and promoter activity analysis showed that the putative DNA binding region at the N-terminus, but not the C-terminal EIL domain, of FimK positively affects transcription of type 1 fimbrial major subunit, fimA. An electrophoretic mobility shift assay demonstrated that the recombinant FimK could specifically bind to fimS, that is located upstream of fimA and contains a vegetative promoter for the fim operon, also reflecting possible transcriptional regulation. EIL_fimK was shown to encode a functional phosphodiesterase (PDE) via enhancing motility in Escherichia coli JM109 and in vitro using PDE activity assays. Moreover, EIL_fimK exhibited higher PDE activity than FimK implying that the N-terminal DNA binding domain may negatively affect the PDE activity of FimK. FimA expression was detected in CG43S3 expressing EIL_fimK or AIL_fimK suggesting that FimA expression is not directly influenced by the c-di-GMP level. In summary, FimK influences type 1 fimbriation by binding to fimS at the N-terminal domain, and thereafter, the altered protein structure may activate C-terminal PDE activity to reduce the intracellular c-di-GMP level.