Effects of Glucose, Vitamins, and DO Concentrations on Pyruvate Fermentation Using Torulopsis glabrata IFO 0005 with Metabolic Flux Analysis

The effects of glucose, vitamins, and DO concentrations on efficient pyruvic acid fermentation were investigated using Torulopsis glabrata IFO 0005, and a novel biphasic culture method was developed on the basis of the metabolic flux analysis. T. glabrata requires the four vitamins nicotinic acid (NA), thiamine hydrochloride (Bi), pyridoxine hydrochloride, and biotin for cell growth. The deficiency of these vitamins plays an essential role in pyruvate fermentation. In the present study, we considered the effects of the first two vitamins on the pyruvate fermentation. On the basis of several batch and fed-batch experiments, it was found that, as a result of glucose inhibition of cell growth, the initial glucose concentration should be around 30—40 g/L, and the glucose concentration during fermentation should be controlled at high level around 30 g/L. On the basis of an analysis of carbon flux distribution, a biphasic fermentation method was developed where the cultivation started with a high DO (at 40—50% of air saturation) for efficient cell growth and then was reduced to 5—10% for efficient pyruvate production. Since a fair amount of ethanol was formed when the DO concentration was decreased, the addition of NA turned out to be effective in reducing the ethanol formation. This may be due to a relaxing of the requirement for NADH oxidation by the alcohol dehydrogenase pathway. Since Bi affects both the pyruvate dehydrogenase complex and pyruvate decarboxylase, its initial concentration must be carefully determined by considering both the cell growth and pyruvate production phases.