title: IscR is essential for yersinia pseudotuberculosis type III secretion and virulence.
abstract: Type III secretion systems (T3SS) are essential for virulence in dozens of pathogens, but are not required for growth outside the host. Therefore, the T3SS of many bacterial species are under tight regulatory control. To increase our understanding of the molecular mechanisms behind T3SS regulation, we performed a transposon screen to identify genes important for T3SS function in the food-borne pathogen Yersinia pseudotuberculosis. We identified two unique transposon insertions in YPTB2860, a gene that displays 79% identity with the E. coli iron-sulfur cluster regulator, IscR. A Y. pseudotuberculosis iscR in-frame deletion mutant (ΔiscR) was deficient in secretion of Ysc T3SS effector proteins and in targeting macrophages through the T3SS. To determine the mechanism behind IscR control of the Ysc T3SS, we carried out transcriptome and bioinformatic analysis to identify Y. pseudotuberculosis genes regulated by IscR. We discovered a putative IscR binding motif upstream of the Y. pseudotuberculosis yscW-lcrF operon. As LcrF controls transcription of a number of critical T3SS genes in Yersinia, we hypothesized that Yersinia IscR may control the Ysc T3SS through LcrF. Indeed, purified IscR bound to the identified yscW-lcrF promoter motif and mRNA levels of lcrF and 24 other T3SS genes were reduced in Y. pseudotuberculosis in the absence of IscR. Importantly, mice orally infected with the Y. pseudotuberculosis ΔiscR mutant displayed decreased bacterial burden in Peyer's patches, mesenteric lymph nodes, spleens, and livers, indicating an essential role for IscR in Y. pseudotuberculosis virulence. This study presents the first characterization of Yersinia IscR and provides evidence that IscR is critical for virulence and type III secretion through direct regulation of the T3SS master regulator, LcrF.
authors.affiliation: Department of Microbiology and Environmental Toxicology, University of California Santa Cruz, Santa Cruz, California, United States of America.
authors.forename: Halie K
authors.initials: HK
authors.lastname: Miller
authors.affiliation: Department of Microbiology and Environmental Toxicology, University of California Santa Cruz, Santa Cruz, California, United States of America.
authors.forename: Laura
authors.initials: L
authors.lastname: Kwuan
authors.affiliation: Department of Microbiology and Environmental Toxicology, University of California Santa Cruz, Santa Cruz, California, United States of America.
authors.forename: Leah
authors.initials: L
authors.lastname: Schwiesow
authors.affiliation: Biomolecular Engineering, University of California Santa Cruz, Santa Cruz, California, United States of America.
authors.forename: David L
authors.initials: DL
authors.lastname: Bernick
authors.affiliation: Department of Biomolecular Chemistry, University of Wisconsin-Madison, Madison, Wisconsin, United States of America.
authors.forename: Erin
authors.initials: E
authors.lastname: Mettert
authors.affiliation: Department of Microbiology and Environmental Toxicology, University of California Santa Cruz, Santa Cruz, California, United States of America.
authors.forename: Hector A
authors.initials: HA
authors.lastname: Ramirez
authors.affiliation: Department of Molecular, Cell, and Developmental Biology, University of California Santa Cruz, Santa Cruz, California, United States of America.
authors.forename: James M
authors.initials: JM
authors.lastname: Ragle
authors.affiliation: Biomolecular Engineering, University of California Santa Cruz, Santa Cruz, California, United States of America.
authors.forename: Patricia P
authors.initials: PP
authors.lastname: Chan
authors.affiliation: Department of Biomolecular Chemistry, University of Wisconsin-Madison, Madison, Wisconsin, United States of America.
authors.forename: Patricia J
authors.initials: PJ
authors.lastname: Kiley
authors.affiliation: Biomolecular Engineering, University of California Santa Cruz, Santa Cruz, California, United States of America.
authors.forename: Todd M
authors.initials: TM
authors.lastname: Lowe
authors.affiliation: Department of Microbiology and Environmental Toxicology, University of California Santa Cruz, Santa Cruz, California, United States of America.
authors.forename: Victoria
authors.initials: V
authors.lastname: Auerbuch
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D058947:Bacterial Secretion Systems / Q000235:genetics*; D001665:Binding Sites / Q000235:genetics; D004251:DNA Transposable Elements / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics; D029968:Escherichia coli Proteins / Q000235:genetics*; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial; D008099:Liver / Q000276:immunology / Q000382:microbiology; D008198:Lymph Nodes / Q000276:immunology / Q000382:microbiology; D051379:Mice; D008969:Molecular Sequence Data; D010581:Peyer's Patches / Q000276:immunology / Q000382:microbiology; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding; D016415:Sequence Alignment; D013154:Spleen / Q000276:immunology / Q000382:microbiology; D014157:Transcription Factors / Q000235:genetics*; D014158:Transcription, Genetic; D059467:Transcriptome / Q000235:genetics; D037521:Virulence Factors / Q000235:genetics*; D015011:Yersinia pseudotuberculosis / Q000235:genetics* / Q000472:pathogenicity*; D015012:Yersinia pseudotuberculosis Infections / Q000276:immunology / Q000473:pathology
chemical_list: D058947:Bacterial Secretion Systems; D004251:DNA Transposable Elements; D029968:Escherichia coli Proteins; C499695:IscR protein, E coli; D014157:Transcription Factors; D037521:Virulence Factors