title: Characterization of a ferrous iron-responsive two-component system in nontypeable Haemophilus influenzae.
abstract: Nontypeable Haemophilus influenzae (NTHI), an opportunistic pathogen that is commonly found in the human upper respiratory tract, has only four identified two-component signal transduction systems. One of these, an ortholog to the QseBC (quorum-sensing Escherichia coli) system, was characterized. This system, designated firRS, was found to be transcribed in an operon with a gene encoding a small, predicted periplasmic protein with an unknown function, ygiW. The ygiW-firRS operon exhibited a unique feature with an attenuator present between ygiW and firR that caused the ygiW transcript level to be 6-fold higher than the ygiW-firRS transcript level. FirRS induced expression of ygiW and firR, demonstrating that FirR is an autoactivator. Unlike the QseBC system of E. coli, FirRS does not respond to epinephrine or norepinephrine. FirRS signal transduction was stimulated when NTHI cultures were exposed to ferrous iron or zinc but was unresponsive to ferric iron. Notably, the ferrous iron-responsive activation only occurred when a putative iron-binding site in FirS and the key phosphorylation aspartate in FirR were intact. FirRS was also activated when cultures were exposed to cold shock. Mutants in ygiW, firR, and firS were attenuated during pulmonary infection, but not otitis media. These data demonstrate that the H. influenzae strain 2019 FirRS is a two-component regulatory system that senses ferrous iron and autoregulates its own operon.
authors.affiliation: Department of Microbiology, University of Kentucky, Lexington, Kentucky, USA.
authors.forename: Kendra H
authors.initials: KH
authors.lastname: Steele
authors.forename: Lauren H
authors.initials: LH
authors.lastname: O'Connor
authors.forename: Nicole
authors.initials: N
authors.lastname: Burpo
authors.forename: Katharina
authors.initials: K
authors.lastname: Kohler
authors.forename: Jason W
authors.initials: JW
authors.lastname: Johnston
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002682:Chinchilla; D003080:Cold Temperature; D005296:Ferrous Compounds / Q000494:pharmacology; D017353:Gene Deletion; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects* / Q000502:physiology*; D049452:Green Fluorescent Proteins; D006192:Haemophilus Infections / Q000382:microbiology; D006193:Haemophilus influenzae / Q000235:genetics / Q000378:metabolism* / Q000472:pathogenicity; D007501:Iron / Q000378:metabolism* / Q000494:pharmacology; D008171:Lung Diseases / Q000382:microbiology; D051379:Mice; D008810:Mice, Inbred C57BL; D009876:Operon / Q000502:physiology; D010033:Otitis Media / Q000382:microbiology; D017354:Point Mutation; D011485:Protein Binding; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014774:Virulence
chemical_list: D001426:Bacterial Proteins; D005296:Ferrous Compounds; D049452:Green Fluorescent Proteins; D007501:Iron; C029451:ferrous chloride