PYRITE OXIDATION BY THIOBACILLUS-FERROOXIDANS WITH SPECIAL REFERENCE TO THE SULFUR MOIETY OF THE MINERAL

Available cultures of Thiobacillus ferrooxidans were found to be contaminated with bacteria very similar to Thiobacillus acidophilus. The experiments described were performed with a homogeneous culture of Thiobacillus ferrooxidans. Pyrite (FeS2) was oxidized by Thiobacillus ferrooxidans grown on iron (Fe2+), elemental sulphur (So) or FeS2. Evidence for the direct utilization of the sulphur moiety of pyrite by Thiobacillus ferrooxidans was derived from the following observations: a. Known inhibitors of Fe2+ and So oxidation, NaN3 and NEM, respectively, partially abolished FeS2 oxidation. b. A b-type cytochrome was detectable in FeS2-and So-grown cells but not in Fe2+-grown cells. c. FeS2 and So reduced b-type cytochromes in whole cells grown on So. d. CO2 fixation at pH 4.0 per mole of oxygen consumed was the highest with So, lowest with Fe2+ and medium with FeS2 as substrate. e. Bacterial Fe2+ oxidation was found to be negligible at pH 5.0 whereas both FeS2 and So oxidation was still appreciable above this pH. f. Separation of pyrite and bacteria by means of a dialysis bag caused a pronounced drop of the oxidation rate which was similar to the reduction of pyrite oxidation by NEM; indirect oxidation of the sulphur moiety by Fe3+ was not affected by separation of pyrite and bacteria. Bacterial oxidation and utilization of the sulphur moiety of pyrite were relatively more important with increasing pH. © 1979 H. Veenman & Zonen B. V.