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

Abstract

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 K. pneumoniae. We found that the CPS amount in K. pneumoniae increased in anaerobic conditions, compared to that in aerobic conditions. An fnr deletion mutant and a site-directed mutant (fnr3CA), 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 cps genes was repressed by holo-FNR. In addition, we found that holo-FNR could repress the transcription of rmpA and rmpA2, encoding cps transcriptional activators. Deletion of rmpA or rmpA2 in the Δfnr strain reduced CPS biosynthesis, suggesting that RmpA and RmpA2 participated in the holo-FNR–mediated repression of cps 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.

Aerobactin Seems To Be a Promising Marker Compared With Unstable RmpA2 for the Identification of Hypervirulent Carbapenem-Resistant Klebsiella pneumoniae: In Silico and In Vitro Evidence

“…The capsule polysaccharide production has three transcription units ( orf1-2 , orf3-15 , and orf16-17 ) in Kp, among which two are directly influenced by rmpA , while one is affected by rmpA2 . The deletion of rmpA and rmpA2 leads to decreased capsular polysaccharide under anaerobic conditions ( Lin et al, 2019 ), which is also observed in the present study. Hence, CR-hvKp that lacks rmpA and rmpA2 lacks hypermucoviscous phenotype due to decreased capsular polysaccharide production.…”

Bactericidal, anti-biofilm, and anti-virulence activity of vitamin C against carbapenem-resistant hypervirulent Klebsiella pneumoniae

“…To further evaluate the anti-virulence activity of VC, the transcriptional responses of both strains KP1088 and hvKP3 in the presence of VC at 4 mg/mL were determined. The rmpA and rmpA2 gene encode capsule biosynthesis and hence the mucoid phenotype in hvKP strains ( Lin et al., 2019 ). According to previous studies, strain KP1088 carried both the rmpA and rmpA2 genes, and that strain hvKP3 carried the rmpA2 gene only ( Gu et al., 2018 ; Zhang et al., 2016a ).…”

First Report of an Extensively Drug-Resistant ST23 Klebsiella pneumoniae of Capsular Serotype K1 Co-Producing CTX-M-15, OXA-48 and ArmA in Spain

“…Plasmid pMS3802-CTXM-vir also encoded some virulence-related genes such as the ferric aerobactin iucABCD and aerobactin receptor iutA, the salmochelin siderophore iroBCDN and truncated copies of genes encoding the capsular polysaccharide synthesis (CPS) regulators rmpA and rmpA2 ( Figure 1 A). According to previous studies, deletions of either rmpA or rmpA2 genes resulted in a significant decrease of CPS [ 9 , 10 , 38 ]. The presence of nonfunctional alleles of these genes might be the cause for the absence of the hypermucoviscous phenotype in isolate MS3802.…”