Thiobacillus ferrooxidans JCM 7811 was cultivated in a basal salts medium containing thiosulfate and ferric ion (Fe
3+).
T. ferrooxidans grew with consuming thiosulfate. Appropriate concentrations of thiosulfate and Fe
3+ were 20 and 30mM, respectively. When
o-phenanthroline, which chelates ferrous ion (Fe
2+), was added to the culture, Fe
2+ reduced from Fe
3+ 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 Fe
2+/mg protein; min. These values were comparable with those of the cells grown on ferrous sulfate. The cell yield against thiosulfate (
Yx/s) was 250×10
8cells/mmol-S
2O
32-, 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.
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