HIGH-DENSITY CULTIVATION OF THIOBACILLUS-THIOOXIDANS S3 IN A FERMENTER WITH CROSS-FLOW FILTRATION

Thiobacillus thiooxidans S3 was cultivated using thiosulfate as an energy source. The thiosulfate showed typical substrate inhibition of the cell growth of T. thiooxidans S3. It was found that the optimum thiosulfate concentration for cell growth was 20 mM. Sodium sulfate (Na2SO4) and potassium sulfate (K2SO4) which accumulated in the culture broth inhibited the thiosulfate oxidation, and thus the cell growth. Fed-batch cultivation with cross-flow filtration allowed continuous removal of inhibitory products such as Na2SO4 and K2SO4, and maintained suitable concentrations of thiosulfate in the culture broth. As a result, T. thiooxidans S3 logarithmically grew up to 7.73 g dry cell weight per liter within 96 h cultivation. The cell productivity (80.5 mg cell/l.h) was 23-fold compared with the batch cultivation.