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Open Access Research article

Role of the small RNA RyhB in the Fur regulon in mediating the capsular polysaccharide biosynthesis and iron acquisition systems in Klebsiella pneumoniae

Su-Hua Huang1, Chien-Kuo Wang1, Hwei-Ling Peng2, Chien-Chen Wu2, Ying-Tsong Chen345, Yi-Ming Hong6 and Ching-Ting Lin6*

Author Affiliations

1 Department of Biotechnology, Asia University, Taichung 41354, Taiwan

2 Department of Biological Science and Technology, National Chiao Tung University, Hsin Chu 30068, Taiwan

3 Institute of Genomics and Bioinformatics, National Chung Hsing University, Tai Chung City 40227, Taiwan

4 Biotechnology Center, National Chung Hsing University, Tai Chung City 40227, Taiwan

5 Institute of Molecular and Genomic Medicine, National Health Research Institutes, Miaoli County 35053, Taiwan

6 School of Chinese Medicine, China Medical University, Taichung 40402, Taiwan

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BMC Microbiology 2012, 12:148  doi:10.1186/1471-2180-12-148

Published: 24 July 2012

Abstract

Background

The capsular polysaccharide (CPS) and iron acquisition systems are important determinants of Klebsiella pneumoniae 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 K. pneumoniae, the role played by RyhB in the Fur regulon has not been characterised. This study investigated Fur regulation of ryhB transcription and the functional role of RyhB in K. pneumoniae.

Results

Deletion of fur from K. pneumoniae increased the transcription of ryhB; the electric mobility shift assay and the Fur-titration assay revealed that Fur could bind to the promoter region of ryhB, suggesting that Fur directly represses ryhB transcription. Additionally, in a Δfur strain with elevated CPS production, deletion of ryhB obviously reduced CPS production. The following promoter-reporter assay and quantitative real-time PCR of cps genes verified that RyhB activated orf1 and orf16 transcription to elevate CPS production. However, deletion of ryhB did not affect the mRNA levels of rcsA, rmpA, or rmpA2. These results imply that Fur represses the transcription of ryhB to mediate the biosynthesis of CPS, which is independent of RcsA, RmpA, and RmpA2. In addition, the Δfur strain’s high level of serum resistance was attenuated by the deletion of ryhB, indicating that RyhB plays a positive role in protecting the bacterium from serum killing. Finally, deletion of ryhB in Δfur reduced the expression of several genes corresponding to 3 iron acquisition systems in K. pneumoniae, and resulted in reduced siderophore production.

Conclusions

The regulation and functional role of RyhB in K. pneumoniae is characterized in this study. RyhB participates in Fur regulon to modulate the bacterial CPS biosynthesis and iron acquisition systems in K. pneumoniae.

Keywords:
RyhB; Fur; Capsular polysaccharide; Iron acquisition system; Klebsiella pneumoniae