Utilization of glucose and cellobiose by Candida wickerhamii

Summary

Candida wickerhamii produced ethanol under aerated and nonaerated conditions when grown on glucose but only under non-aerated conditions when grown on cellobiose. When the yeast was grown on 20 g·l⁻¹ glucose in fermentation flasks, the substrate was completely utilized and 9.2 g·l⁻¹ ethanol was produced. When 100 g·l⁻¹ glucose was used, only 60% of the substrate was consumed and 23.4 g·l⁻¹ ethanol was produced fermentatively whereas 31 g·l⁻¹ ethanol was produced in an aerated fermenter. Ethanol toxicity was confirmed by adding ethanol to the culture. No ethanol was produced at added ethanol concentrations of 24 g·l⁻¹ or higher although growth occurred even in the presence of 74 g·l⁻¹ ethanol. The fermentation of glucose and cellobiose (20 g·l⁻¹) was completed in 24 h and 125 h with specific growth rates of 0.29 and 0.06 h⁻¹ respectively. β-Glucosidase was produced when grown on either glucose or cellobiose but the differential rate of enzyme production was 64 fold higher on cellobiose. Increased aeration stimulated enzyme production. β-Glucosidase was present in the fermentation broth and associated with the cells under non-aerated conditions and almost exclusively cell-associated under aerated conditions.