Abstract
The chemical attack of ore by ferric iron and/or sulfuric acid releases valuable metals. The products of these reactions are recycled by iron and sulfur oxidizing microorganisms. These acidophilic chemolithotrophic prokaryotes, among which Acidithiobacillus ferrooxidans, grow at the expense of the energy released from the oxidation of ferrous iron and/or inorganic sulfur compounds (ISCs). In At. ferrooxidans, it has been shown that the expression of the genes encoding the proteins involved in these respiratory pathways is dependent on the electron donor and that the genes involved in iron oxidation are expressed before those responsible for ISCs oxidation when both iron and sulfur are present. Since the redox potential increases during iron oxidation but remains stable during sulfur oxidation, we have put forward the hypothesis that the global redox responding two components system RegB/RegA is involved in this regulation. To understand the mechanism of this system and its role in the regulation of the aerobic respiratory pathways in At. ferrooxidans, the binding of different forms of RegA (DNA binding domain, wild-type, unphosphorylated and phosphorylated-like forms of RegA) on the regulatory region of different genes/operons involved in ferrous iron and ISC oxidation has been analyzed. We have shown that the four RegA forms are able to bind specifically the upstream region of these genes. Interestingly, the phosphorylation of RegA did not change its affinity for its cognate DNA. The transcriptional start site of these genes/operons has been determined. In most cases, the RegA binding site(s) was (were) located upstream from the −35 (or −24) box suggesting that RegA does not interfere with the RNA polymerase binding. Based on the results presented in this report, the role of the RegB/RegA system in the regulation of the ferrous iron and ISC oxidation pathways in At. ferrooxidans is discussed.
Highlights
Among the biomining microorganisms, the strict acidophilic chemolithoautotrophic bacterium Acidithiobacillus ferrooxidans, that obtains its energy from the oxidation of ferrous iron [Fe(II)] and inorganic sulfur compounds (ISCs), is considered as a model
RegA-HTH and Full-Length RegA Bind to the Regulatory Region of Several Genes/Operons Involved in Fe(II) and Inorganic Sulfur Compound Oxidation
We have previously shown by Electrophoretic Mobility Shift Assays (EMSA) that a preparation enriched in recombinant RegA tagged at its C-terminus with six histidines was able to bind to the regulatory region of the genes involved in Fe(II) and ISCs oxidation which expression depends on the electron donor present in the medium (Sandoval Ponce et al, 2012)
Summary
The strict acidophilic chemolithoautotrophic bacterium Acidithiobacillus ferrooxidans, that obtains its energy from the oxidation of ferrous iron [Fe(II)] and inorganic sulfur compounds (ISCs), is considered as a model. The expression of the genes involved in these respiratory systems is regulated according to the available electron donor in the environment i.e., the genes involved in Fe(II) oxidation are more expressed in Fe(II)- than in sulfurgrown cells and vice-versa, those involved in ISCs oxidation are preferentially transcribed in the presence of sulfur than Fe(II) (Yarzabal et al, 2004; Quatrini et al, 2006, 2009; Bruscella et al, 2007; Sandoval Ponce et al, 2012) When both Fe(II) and sulfur are present in the medium, Fe(II) is immediately oxidized while sulfur oxidation takes place only after Fe(II) was completely oxidized to ferric iron [Fe(III); (Yarzabal et al, 2004; Sandoval Ponce et al, 2012)]. The expression of the genes involved in Fe(II) and ISCs oxidation appears to depend on the oxidation state of iron [Fe(II) or Fe(III)] present in the medium
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