title: IscR Regulates Synthesis of Colonization Factor Antigen I Fimbriae in Response to Iron Starvation in Enterotoxigenic Escherichia coli.
abstract: Iron availability functions as an environmental cue for enteropathogenic bacteria, signaling arrival within the human host. As enterotoxigenic Escherichia coli (ETEC) is a major cause of human diarrhea, the effect of iron on ETEC virulence factors was evaluated here. ETEC pathogenicity is directly linked to production of fimbrial colonization factors and secretion of heat-labile enterotoxin (LT) and/or heat-stable enterotoxin (ST). Efficient colonization of the small intestine further requires at least the flagellin binding adhesin EtpA. Under iron starvation, production of the CFA/I fimbriae was increased in the ETEC H10407 prototype strain. In contrast, LT secretion was inhibited. Furthermore, under iron starvation, gene expression of the cfa (CFA/I) and etp (EtpBAC) operons was induced, whereas transcription of toxin genes was either unchanged or repressed. Transcriptional reporter fusion experiments focusing on the cfa operon further showed that iron starvation stimulated cfaA promoter activity in ETEC, indicating that the impact of iron on CFA/I production was mediated by transcriptional regulation. Evaluation of cfaA promoter activity in heterologous E. coli single mutant knockout strains identified IscR as the regulator responsible for inducing cfa fimbrial gene expression in response to iron starvation, and this was confirmed in an ETEC ΔiscR strain. The global iron response regulator, Fur, was not implicated. IscR binding sites were identified in silico within the cfaA promoter and fixation confirmed by DNase I footprinting, indicating that IscR directly binds the promoter region to induce CFA/I.
  
  
  OBJECTIVE
  Pathogenic enterobacteria modulate expression of virulence genes in response to iron availability. Although the Fur transcription factor represents the global regulator of iron homeostasis in Escherichia coli, we show that several ETEC virulence factors are modulated by iron, with expression of the major fimbriae under the control of the iron-sulfur cluster regulator, IscR. Furthermore, we demonstrate that the apo form of IscR, lacking an Fe-S cluster, is able to directly fix the corresponding promoter region. These results provide further evidence implicating IscR in bacterial virulence and suggest that IscR may represent a more general regulator mediating the iron response in enteropathogens.
authors.affiliation: Research Department, Sanofi Pasteur, Marcy-l'Étoile, France UMR5240 CNRS/INSA/UCB, Université de Lyon, Villeurbanne, France, and INSA de Lyon, Villeurbanne, France.
authors.forename: Sara
authors.identifier: http://orcid.org/0000-0002-4454-1584
authors.initials: S
authors.lastname: Haines
authors.affiliation: Research Department, Sanofi Pasteur, Marcy-l'Étoile, France.
authors.forename: Nadège
authors.initials: N
authors.lastname: Arnaud-Barbe
authors.affiliation: Research Department, Sanofi Pasteur, Marcy-l'Étoile, France.
authors.forename: David
authors.initials: D
authors.lastname: Poncet
authors.affiliation: UMR5240 CNRS/INSA/UCB, Université de Lyon, Villeurbanne, France, and INSA de Lyon, Villeurbanne, France.
authors.forename: Sylvie
authors.initials: S
authors.lastname: Reverchon
authors.affiliation: UMR5240 CNRS/INSA/UCB, Université de Lyon, Villeurbanne, France, and INSA de Lyon, Villeurbanne, France.
authors.forename: Julien
authors.initials: J
authors.lastname: Wawrzyniak
authors.affiliation: UMR5240 CNRS/INSA/UCB, Université de Lyon, Villeurbanne, France, and INSA de Lyon, Villeurbanne, France.
authors.forename: William
authors.initials: W
authors.lastname: Nasser
authors.affiliation: Research Department, Sanofi Pasteur, Marcy-l'Étoile, France genevieve.renauld@sanofipasteur.com.
authors.forename: Geneviève
authors.initials: G
authors.lastname: Renauld-Mongénie
mesh_terms: D001427:Bacterial Toxins / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites; D054307:Enterotoxigenic Escherichia coli / Q000378:metabolism*; D004768:Enterotoxins / Q000235:genetics / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D036781:Fimbriae Proteins / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects / Q000502:physiology*; D007501:Iron / Q000494:pharmacology*; D011401:Promoter Regions, Genetic; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D037521:Virulence Factors / Q000235:genetics / Q000378:metabolism
chemical_list: D001427:Bacterial Toxins; D004768:Enterotoxins; D029968:Escherichia coli Proteins; C499695:IscR protein, E coli; D014157:Transcription Factors; D037521:Virulence Factors; C022924:colonization factor antigens; D036781:Fimbriae Proteins; C027538:heat-labile enterotoxin, E coli; D007501:Iron