Genes involved in iron and sulfur oxidation pathways in Acidithiobacillus ferrooxidans are regulated by ferrous iron and the global redox responding regBA two component system

摘要

The bioleaching bacterium Acidithiobacillus ferrooxidans oxidizes ferrous iron (Fe ( II )) and reduced inorganic sulfur compounds (RISC) in oxic conditions. The genes involved in these reactions have been identified in the type strain, ATCC 23270. It was shown that the genes involved in Fe ( II ) oxidation are expressed preferentially in the presence of Fe( II ) than sulfur and those involved in RISCs oxidation are more transcribed in sulfurthan in Fe( II )-grown cells. Oxidation of Fe( II ) and sulfur has been followed when both electron donors are present in the medium. The results obtained indicate that At. ferrooxidans oxidizes Fe ( II ) first and that sulfur oxidation takes place only when iron is totally oxidized. In agreement with these data, the genes involved in Fe ( II ) are expressed before those involved in RISC oxidation, even in the presence of sulfur. Therefore, it appears that the genes involved in RISC oxidation are repressed in the presence of Fe ( II ) suggesting that a regulator is likely involved in switching on the genes involved in Fe( II ) oxidation and in switching off the genes involved in RISC oxidation when Fe ( II ) is present. One possible candidate belongs to the sensor/regulator two-component signal transducing system of the regB/regA family involved in redox sensing. The regBA operon has a similar response to Fe( H ) and sulfur as the genes involved in Fe( H ) oxidation, that is Fe( II ) induction and no sulfur repression. The regulator regA is able to bind to the regulatory region of a number of genes/operons which expression is regulated by Fe( II ), and could therefore play a role in switching from Fe( II ) to sulfur oxidation after Fe( II ) has been depleted. The understanding of how regBA controls the energetic pathways depending on the overall redox state of the cell is of primordial importance for bioleaching since it could help controlling the dynamics of Fe( II ) and RISC oxidation.