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.

Regulation of Iron Metabolism by Pyrococcus furiosus

“…It has been reported that the global transcription profiles of the hyperthermophilic archaeon Thermococcus kodakarensis, a close relative of P. furiosus, were similar under iron-sufficient and iron-limited conditions, suggesting a lessthan-stringent response to iron availability (14). Similar nonresponsive transcriptional effects of iron were also observed with the obligately anaerobic and mesophilic bacteria Coxiella burnetii and Dichelobacter nodosus (15,16).…”

“…Similar results have been reported for several other anaerobes. The pathogenic bacterium Coxiella burnetii lacks annotated iron acquisition and storage systems, and its Fur regulon consists of three genes (the iron transporter gene feoB, a gene encoding a putative cation efflux protein, and a gene predicted to encode an iron-binding protein) (15), indicating that iron-dependent transcriptional regulation plays a minor role in iron metabolism. In Dichelobacter nodosus, the Fur regulon includes genes encoding two putative iron transporters (YfeA and CbiK) and a manganese superoxide dismutase (SodA) (16).…”

“…It has been reported that the global transcription profiles of the hyperthermophilic archaeon Thermococcus kodakarensis, a close relative of P. furiosus, were similar under iron-sufficient and iron-limited conditions, suggesting a lessthan-stringent response to iron availability (14). Similar nonresponsive transcriptional effects of iron were also observed with the obligately anaerobic and mesophilic bacteria Coxiella burnetii and Dichelobacter nodosus (15,16).To study the regulation of iron metabolism in P. furiosus, we first searched its genome for genes encoding potential iron-responsive transcriptional regulators. Homologs of the bacterial transcription factors Fur and DtxR were found, while homologs of other previously identified regulators, including RirA, Rrf2, Aft1, Aft2, and IRP,.…”

Sex-Related Differences in Gene Expression Following Coxiella burnetii Infection in Mice: Potential Role of Circadian Rhythm

“…Hepcidins (Hamp1 and Hamp2) reduce iron availability for invading microorganisms by reducing extracellular iron concentrations [35]. As has been recently suggested, greater iron availability in males may favor C. burnetii replication [36]. It has also been shown that hepcidins are differentially expressed in male and female mice [37], [38].…”

Genetics of Coxiella Burnetii : On the Path of Specialization

“…The bacterium also possesses thiamine pyrophosphate and flavin mononucleotide riboswitches, which can regulate gene expression by sensing the levels of their cognate molecules [95]. Although iron is not believed to play an important role in virulence, a Fur-based regulatory system that detects and responds to iron concentrations is also present [96]. It has also been shown that Coxiella modulates the autophagic pathway in host cells, probably to compensate for a lack of nutrients within the PV [97].…”