Acquisition of regulator on virulence plasmid of hypervirulent Klebsiella allows bacterial lifestyle switch in response to iron

Abstract

Hypervirulent Klebsiella pneumoniae causes liver abscess and potentially devastating metastatic complications. The majority of Klebsiella -induced liver abscess are caused by the CG23-I sublineage of hypervirulent Klebsiella pneumoniae . This and some other lineages possess a >200-kb virulence plasmid. We discovered a novel protein IroP nestled in the virulence plasmid-encoded salmochelin operon that cross-regulates and suppresses the promoter activity of chromosomal type 3 fimbriae (T3F) gene transcription. IroP is itself repressed by iron through the ferric uptake regulator. Iron-rich conditions increase T3F and suppress capsule mucoviscosity, leading to biofilm formation and cell adhesion. Conversely, iron-poor conditions cause a transcriptional switch to hypermucoid capsule production and T3F repression. The likely acquisition of iroP on mobile genetic elements and successful adaptive integration into the genetic circuitry of a major lineage of hypervirulent K. pneumoniae reveal a powerful example of plasmid chromosomal cross talk that confers an evolutionary advantage. Our discovery also addresses the conundrum of how the hypermucoid capsule that impedes adhesion could be regulated to facilitate biofilm formation and colonization. The acquired ability of the bacteria to alternate between a state favoring dissemination and one that favors colonization in response to iron availability through transcriptional regulation offers novel insights into the evolutionary success of this pathogen. IMPORTANCE Hypervirulent Klebsiella pneumoniae contributes to the majority of monomicrobial-induced liver abscess infections that can lead to several other metastatic complications. The large virulence plasmid is highly stable in major lineages, suggesting that it provides survival benefits. We discovered a protein IroP encoded on the virulence plasmid that suppresses expression of the type 3 fimbriae. IroP itself is regulated by iron, and we showed that iron regulates hypermucoid capsule production while inversely regulating type 3 fimbriae expression through IroP. The acquisition and integration of this inverse transcriptional switch between fimbriae and capsule mucoviscosity shows an evolved sophisticated plasmid-chromosomal cross talk that changes the behavior of hypervirulent K. pneumoniae in response to a key nutrient that could contribute to the evolutionary success of this pathogen.

Inorganic Polyphosphate Affects Biofilm Assembly, Capsule Formation, and Virulence of Hypervirulent ST23 Klebsiella pneumoniae

“…A recent report has suggested that the coexistence of c-rmpA with p-rmpA and p-rmpA2 increases the lethality of K1 K. pneumoniae strains and the development of hepatic abscesses more than the coexistence of siderophores. 74 Each virulence factor present in K. pneumoniae participates in the infectious process depending on external signals, as in the case of the recently described iroP switch, 75 where iron favors biofilm formation in iron-rich environments such as the intestine while reducing capsule production. Therefore, in our virulence model, the capsule becomes highly relevant as a mechanism used by hvKP strains to evade phagocytosis.…”

“…Each virulence factor present in K. pneumoniae participates in the infectious process depending on external signals, as in the case of the recently described iroP switch, where iron favors biofilm formation in iron-rich environments such as the intestine while reducing capsule production. Therefore, in our virulence model, the capsule becomes highly relevant as a mechanism used by hvKP strains to evade phagocytosis.…”

Effects of Polyphosphate metabolism Mutations on Biofilm, Capsule Formation and Virulence Traits in Hypervirulent ST23Klebsiella pneumoniaeSGH10

“…Recently, a phenotypic switch between type III fimbriae and the hypermucoviscous capsule in response to iron levels has been reported in the SGH10 strain. 70,27 The iron-regulated outer membrane protein IroP, encoded in the virulence plasmid, inhibits the expression of the mrk operon under low iron conditions, promoting biofilm formation. Since polyphosphates (polyP) are directly involved in intracellular iron homeostasis 74 , the observed alterations in the capsule and biofilm might be related to this recently described phenomenon.…”

“…In the context of K. pneumoniae and polyP metabolism, the effect of gallein, an inhibitor of polyP synthesis, has been studied, revealing a concentration-dependent decrease in biofilm formation 26 . hvKP strains are associated with enhanced virulence and have been observed to form biofilms and produce a protective capsule, contributing to their pathogenicity 27 . However, the precise mechanism by which polyP metabolism and PPK1 influence Klebsiella virulence remains poorly understood.…”

Emergence of novel non-aggregative variants under negative frequency-dependent selection in Klebsiella variicola

“…It could also be that in these strains, T3F is regulated differently. In the specific case of hypervirulent strains, characterized by the presence of the virulence plasmid encoding rmpA , but also other siderophores like salmochelin ( iro operon) and aerobactin ( iuc operon), it was recently shown that T3F and capsule are both tightly regulated by iroP also present in the virulence plasmid (Chu et al 2023 ). IroP acts as a switch, by which T3F is repressed during capsule expression.…”