Objective      To determine the effect of rcsB gene on hypermucoviscosity and biofilm formation ability of Klebsiella pneumoniae by constructing unmarked rcsB-deletion mutant and rcsB complementation strain.       Methods      First

unmarked rcsB-deletion mutant was constructed. The upstream and downstream flanking DNA fragments of rcsB gene were amplified by PCR and then cloned into plasmid pKO3-Km. The recombinant plasmid was transferred into Klebsiella pneumoniae NTUH-K2044. After homologous recombination

unmarked rcsB-deletion mutant was screened. Second

the complementation strain was constructed. The rcsB fragment was amplified and cloned into plasmid pBAD33

and then the recombinant plasmid was transferred into rcsB-deletion mutant to get the complementation strain. The hypermucoviscosity and biofilm formation ability were tested.       Results      The unmarked rcsB-deletion mutant and complementation strain were constructed successfully. The results showed that the hypermucoviscosity and biofilm formation ability of the mutant were decreased

while the hypermucoviscosity and biofilm formation of the complementation strain was between the wild strain and the mutant.       Conclusion      The transcription factor RcsB positively regulates the hypermucoviscosity and biofilm formation ability of Klebsiella pneumonia.