Differential fructose effect in Pachysolen tannophilus and Pichia stipitis

The yeasts Pachysolen tannophilus and Pichia stipitis differed in their ability to utilize d ‐xylose in the presence of d ‐fructose. When P. tannophilus was grown aerobically in a fructose‐xylose mixture, the ketohexose was utilized preferentially over the pentose. However, in P. stipitis cultures, the converse was observed. The effect was associated with the ability of d ‐fructose to repress the induction of xylose reductase and xylitol dehydrogenase activities in P. tannophilus but not in P. stipitis . Both yeasts grew on d ‐fructose and fermented it to ethanol when it was supplied as the sole carbon source. The results suggest that there may exist some fundamental difference in the regulation of d ‐fructose metabolism between P. tannophilus and P. stipitis .