THE INFLUENCE OF COSUBSTRATE AND AERATION ON XYLITOL FORMATION BY RECOMBINANT SACCHAROMYCES-CEREVISIAE EXPRESSING THE XYL1 GENE

Xylitol formation by a recombinant Saccharomyces cerevisiae strain con taining the XYL1 gene from Pichia stipitis CBS 6054 was investigated u nder three sets of conditions: (a) with glucose, ethanol, acetate, or glycerol as cosubstrates, (b) with different oxygenation levels, and ( c) with different ratios of xylose to cosubstrate. With both glucose a nd ethanol the conversion yields were close to 1 g xylitol/g consumed xylose. Decreased aeration increased the xylitol yield on the basis of consumed cosubstrate, while the rate of xylitol formation decreased. The xylitol yield based on consumed cosubstrate also increased with in creased xylose:cosubstrate ratios. The transformant utilized the cosub strate more efficiently than did a reference strain in terms of utiliz ation rate and growth rate, implying that the regeneration of NAD(P)() during xylitol formation by the transformant balanced the intracellu lar redox potential.