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

Thiobacillus ferrooxidans JCM 7811 was cultivated in a basal salts med ium 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 f rom Fe3+ was gradually accumulated. In the cultures with 25 and 50mM o f o-phenanthroline, the bacterial growth and thiosulfate consumption w ere inhibited. These results indicated that thiosulfate was oxidized t hrough the sulfur oxidation route with a ferric ion-reducing (FIR) sys tem. During 5 days of cultivation, the cells grew up to 5.0 X 10(8) ce lls/ml, and the grown cells had the iron oxidizing activity of 2.2 mu mol 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 X 10(8) cells/mmol-S2O32-, which was about 20-fold hig her than that against ferrous sulfate. Iron ions were cyclically utili zed in the FIR system, therefore, the usage of ferrous sulfate could b e reduced to obtain a desired cell mass.