GROWTH OF THIOBACILLUS FERROOXIDANS UTILIZED THIOSULFATE THROUGH THE OXIDATION ROUTE WITH IRON RECYCLING

Abstract

Thiobacillus ferrooxidans JCM 7811 was cultivated in a basal salts medium containing thiosulfate and ferric ion (Fe³⁺). T. ferrooxidans grew with consuming thiosulfate. Appropriate concentrations of thiosulfate and Fe³⁺ were 20 and 30mM, respectively. When o-phenanthroline, which chelates ferrous ion (Fe²⁺), was added to the culture, Fe²⁺ reduced from Fe³⁺ was gradually accumulated. In the cultures with 25 and 50mM of o-phenanthroline, the bacterial growth and thiosulfate consumption were inhibited. These results indicated that thiosulfate was oxidized through the sulfur oxidation route with a ferric ion-reducing (FIR) system. During 5 days of cultivation, the cells grew up to 5.0×108 cells/ml, and the grown cells had the iron oxidizing activity of 2.2μmol Fe²⁺/mg protein; min. These values were comparable with those of the cells grown on ferrous sulfate. The cell yield against thiosulfate (Yx/s) was 250×10⁸cells/mmol-S₂O₃^2-, which was about 20-fold higher than that against ferrous sulfate. Iron ions were cyclically utilized in the FIR system, therefore, the usage of ferrous sulfate could be reduced to obtain a desired cell mass.