Physiological Properties of a Mutant of Pachysolen tannophilus Deficient in NADPH-Dependent d -Xylose Reductase

Abstract

A d -xylose reductase mutant of Pachysolen tannophilus was isolated on the basis of its poor growth on d -xylose but normal growth on xylitol and d -glucose. Fractionation of cell extracts indicated that the mutant was deficient in d -xylose reductase activity that used NADPH exclusively as a cofactor, but not in activity that used both NADH and NADPH. Mutant cultures grown on d -xylose as the sole carbon source exhibited some properties that would be desired in improved strains. Growth rate, growth yield, and d -xylose consumption rate of the mutant were less sensitive than those of the wild type to changes in aeration rate. d -Xylose was utilized more efficiently in that less of a by-product, xylitol, was produced. In addition, under low aeration conditions, more ethanol was produced. A disadvantage was a relatively slow rate of d -xylose utilization.