AUTHOR=Lin Tien-Huang , Wu Chien-Chen , Kuo Jong-Tar , Chu Hsu-Feng , Lee Ding-Yu , Lin Ching-Ting 

TITLE=FNR-Dependent RmpA and RmpA2 Regulation of Capsule Polysaccharide Biosynthesis in Klebsiella pneumoniae

JOURNAL=Frontiers in Microbiology

VOLUME=10

YEAR=2019

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2019.02436

DOI=10.3389/fmicb.2019.02436

ISSN=1664-302X

ABSTRACT=<p>Fumarate nitrate reduction regulator (FNR) is a direct oxygen-responsive transcriptional regulator containing an iron-sulfur (Fe–S) cluster. During anaerobic growth, the [4Fe–4S] cluster in FNR (holo-FNR) binds specifically to DNA, whereas exposure to oxygen results in the loss of its DNA-binding activity via oxidation of the [4Fe–4S] cluster. In this study, we aimed to investigate the role of FNR in regulation of capsular polysaccharide (CPS) biosynthesis, serum resistance, and anti-phagocytosis of <italic>K. pneumoniae</italic>. We found that the CPS amount in <italic>K. pneumoniae</italic> increased in anaerobic conditions, compared to that in aerobic conditions. An <italic>fnr</italic> deletion mutant and a site-directed mutant (<italic>fnr</italic><sub>3</sub><sub>CA</sub>), with the three cysteines (C20, C23, and C29) replaced with alanines to mimic an FNR lacking the [4Fe-4S] cluster, showed marked increase in CPS amount under anaerobic conditions. A promoter-reporter assay and qRT-PCR confirmed that the transcription of the <italic>cps</italic> genes was repressed by holo-FNR. In addition, we found that holo-FNR could repress the transcription of <italic>rmpA</italic> and <italic>rmpA2</italic>, encoding <italic>cps</italic> transcriptional activators. Deletion of <italic>rmpA</italic> or <italic>rmpA2</italic> in the Δ<italic>fnr</italic> strain reduced CPS biosynthesis, suggesting that RmpA and RmpA2 participated in the holo-FNR–mediated repression of <italic>cps</italic> transcription, thereby regulating the CPS amount, serum resistance, and anti-phagocytosis. Taken together, our results provided evidence that RmpA and RmpA2 participated in the holo-FNR–mediated repression of CPS biosynthesis, and resistance to the host defense in response to oxygen availability.</p>