| Summary: | <p>Abstract</p> <p>Background</p> <p>The capsular polysaccharide (CPS) and iron acquisition systems are important determinants of <it>Klebsiella pneumoniae</it> infections, and we have previously reported that the ferric uptake repressor (Fur) can play dual role in iron acquisition and CPS biosynthesis. In many bacteria, Fur negatively controls the transcription of the small non-coding RNA RyhB to modulate cellular functions and virulence. However, in <it>K. pneumoniae</it>, the role played by RyhB in the Fur regulon has not been characterised. This study investigated Fur regulation of <it>ryhB</it> transcription and the functional role of RyhB in <it>K. pneumoniae</it>.</p> <p>Results</p> <p>Deletion of <it>fur</it> from <it>K. pneumoniae</it> increased the transcription of <it>ryhB</it>; the electric mobility shift assay and the Fur-titration assay revealed that Fur could bind to the promoter region of <it>ryhB</it>, suggesting that Fur directly represses <it>ryhB</it> transcription. Additionally, in a Δ<it>fur</it> strain with elevated CPS production, deletion of <it>ryhB</it> obviously reduced CPS production. The following promoter-reporter assay and quantitative real-time PCR of <it>cps</it> genes verified that RyhB activated <it>orf1</it> and <it>orf16</it> transcription to elevate CPS production. However, deletion of <it>ryhB</it> did not affect the mRNA levels of <it>rcsA</it>, <it>rmpA</it>, or <it>rmpA2</it>. These results imply that Fur represses the transcription of <it>ryhB</it> to mediate the biosynthesis of CPS, which is independent of RcsA, RmpA, and RmpA2. In addition, the Δ<it>fur</it> strain’s high level of serum resistance was attenuated by the deletion of <it>ryhB</it>, indicating that RyhB plays a positive role in protecting the bacterium from serum killing. Finally, deletion of <it>ryhB</it> in Δ<it>fur</it> reduced the expression of several genes corresponding to 3 iron acquisition systems in <it>K. pneumoniae,</it> and resulted in reduced siderophore production<it>.</it></p> <p>Conclusions</p> <p>The regulation and functional role of RyhB in <it>K. pneumoniae</it> is characterized in this study. RyhB participates in Fur regulon to modulate the bacterial CPS biosynthesis and iron acquisition systems in <it>K. pneumoniae</it>.</p>
|
|---|