title: Limited role for iron regulation in Coxiella burnetii pathogenesis.
abstract: In gram-negative bacteria, iron acquisition proteins are commonly regulated by Fur (ferric uptake regulator), which binds iron-regulated promoters (the Fur box). We hypothesized that Coxiella burnetii requires iron and employs an iron-regulatory system and used various approaches to define a Fur regulon. Cloned C. burnetii fur complemented an Escherichia coli fur deletion mutant. A ferrous iron transporter gene (CBU1766), a putative iron binding protein-encoding gene (CBU0970), and a cation efflux pump gene (CBU1362) were identified by genome annotation and using a Fur titration assay. Bioinformatically predicted Fur box-containing promoters were tested for transcriptional control by iron. Five genes demonstrated at least a twofold induction with minimal iron. Putatively regulated genes were evaluated in a two-plasmid regulator/promoter heterologous expression system. These data suggested a very limited Fur-regulated system in C. burnetii. In an in vitro tissue culture model, a significant increase in bacterial growth was observed with infected cells treated with deferoxamine in comparison to growth under iron-replete conditions. In an iron-overloaded animal model in vivo, the level of bacterial growth detected in the iron-injected animals was significantly decreased in comparison to growth in control animals. In a low-iron-diet animal model, a significant increase in splenomegaly was observed, but no significant change in bacterial growth was identified. The small number of predicted iron acquisition systems, few Fur-regulated genes, and enhanced replication under a decreased iron level predict a requirement of a low level of iron for survival, perhaps to avoid creation of additional reactive oxygen radicals.
authors.affiliation: Department of Microbial and Molecular Pathogenesis, Texas A&M University System Health Science Center, College Station, TX 77843-1114, USA.
authors.forename: Heather L
authors.initials: HL
authors.lastname: Briggs
authors.forename: Nicolein
authors.initials: N
authors.lastname: Pul
authors.forename: Rekha
authors.initials: R
authors.lastname: Seshadri
authors.forename: Mary J
authors.initials: MJ
authors.lastname: Wilson
authors.forename: Claudia
authors.initials: C
authors.lastname: Tersteeg
authors.forename: Kasi E
authors.initials: KE
authors.lastname: Russell-Lodrigue
authors.forename: Masako
authors.initials: M
authors.lastname: Andoh
authors.forename: Andreas J
authors.initials: AJ
authors.lastname: Bäumler
authors.forename: James E
authors.initials: JE
authors.lastname: Samuel
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000502:physiology; D001665:Binding Sites; D027682:Cation Transport Proteins / Q000096:biosynthesis / Q000235:genetics; D002460:Cell Line; D015169:Colony Count, Microbial / Q000379:methods; D016997:Coxiella burnetii / Q000254:growth & development / Q000378:metabolism* / Q000472:pathogenicity*; D003676:Deferoxamine / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics; D005260:Female; D017353:Gene Deletion; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial; D005816:Genetic Complementation Test; D007501:Iron / Q000378:metabolism*; D033862:Iron-Binding Proteins / Q000096:biosynthesis / Q000235:genetics; D008264:Macrophages / Q000382:microbiology*; D051379:Mice; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D011778:Q Fever / Q000382:microbiology*; D018085:Regulon; D012097:Repressor Proteins / Q000235:genetics / Q000502:physiology; D017386:Sequence Homology, Amino Acid
chemical_list: D001426:Bacterial Proteins; D027682:Cation Transport Proteins; D033862:Iron-Binding Proteins; D012097:Repressor Proteins; C068477:ferric uptake regulating proteins, bacterial; D007501:Iron; D003676:Deferoxamine