Table 2.

Examples of iron-dependent redox sensor proteins in bacteria. (*) The references given are for the protein from the strain listed. Sequence alignments demonstrate that highly homologous proteins are found across many different bacterial species.

	Name	Strain*	Function
Transcriptional regulator	Fur	Escherichia coli	Regulator with iron-dependent DNA-binding affinity negatively regulates genes involved in ferric iron uptake [38].
	DtxR	Corynebacterium glutamicum	DtxR acts as a global iron-mediated regulator, activating genes involved in iron storage and DNA protection and repressing genes involved in iron uptake and utilization [39].
	RirA	Rhizobium leguminosarum	Transcriptional regulator RirA is involved in ferric uptake regulation by regulating genes coding for iron transport, siderophore biosynthesis, and iron-sulfur cluster assembly [40].
	Irr	Bradyrhizobium japonicum	Iron response regulator (Irr) senses iron through the status of heme biosynthesis to regulate gene expression involved in iron homeostasis [42].
	PerR	Bacillus subtilis	DNA binding by the regulator PerR in response to peroxide stress is iron dependent [51].
	DmdR1	Streptomyces coelicolor	The transcriptional regulator DmdR1 regulates genes involved in desferrioxamine production in response to iron availability [43].
	IdeR	Mycobacterium smegmatis	IdeR negatively regulates siderophore biosynthesis involved in iron acquisition [44].
	SirR	Staphylococcus epidermidis	SirR is a Fe2+or Mn2+-dependent transcriptional repressor regulating the sitABC operon encoding an ATPase, a cytoplasmic membrane protein, and the 32-kDa lipoprotein involved in siderophore-mediated iron uptake [45].
	FNR	Escherichia coli	Transcription factor FNR regulates gene expression in response to oxygen deficiency by its redox-sensitive bound iron. Binding of an iron-sulfur cluster is required for a conformational change to enhance DNA binding [46].
	IscR	Escherichia coli	[2Fe-2S]-cluster assembly regulates activity in transcription factor IscR of genes coding for proteins involved in iron-sulfur cluster assembly [47].
	TroR	Treponema denticola	TroR is a Mn2+ and Fe2+-dependent repressor of the ATP-binding cassette cation transport system (troABCD) regulating manganese and iron homeostasis [50].
Regulatory element	HbpS/SenS/SenR	Streptomyces reticuli	Iron-dependent activation/inhibition of the two-component system SenS-SenR involved in oxidative stress response through heme degradation and associated secondary structural changes [8].
	PmrA/PmrB	Salmonella enterica	The PmrA/PmrB two-component system senses iron and regulates the transcription of genes involved in iron resistance [41].
	ChrS/ChrA	Corynebacterium diphteriae	ChrS, the heme-sensing sensor kinase of the two-component system ChrS/ChrA, regulates genes involved in utilization of host heme as an iron source and in protecting the bacteria against the toxic effects of heme [48].
	FecA/FecR/FecI	Escherichia coli	The periplasmic protein FecR senses periplasmic iron dicitrate by the outer membrane protein FecA which is loaded with ferric citrate. FecR transmits the signal to the sigma factor FecI which results in transcriptional activation of the fec-operon for ferric citrate transport [52].
	AcnA/AcnB	Escherichia coli	The aconitases AcnA (induced by iron and oxidative stress) and AcnB posttranscriptionally regulate gene expression (i.e., sodA) by an iron-sulfur cluster-dependent switch [49].