Electron shuttles stimulate the reductive dissolution of jarosite by Acidiphilium cryptum

Jarosite is stable under oxidizing conditions at low pH, but Acidiphilium cryptum can promote its reductive dissolution to Fe(II). Since electron shuttles enhance the bioreduction of iron oxides at circumneutral pH, nine compounds were selected to study their effect on jarosite dissolution at low pH. Gallocyanine, methylene blue and thionine stimulated the bioreduction of jarosite by factors of four, six and ten, respectively. Cyclic voltammetry test at pH 2.5 showed that these three compounds have a half-wave potential in the range 276–375 mV vs SHE. Similar results have been reported for neutrophiles, although the range obtained in this work was shifted to positive values. This behavior would be related to the ability of A. cryptum to reduce electron shuttles and thermodynamic data for reduction of ferric compounds.