Yeasts were grown on YEPX agar plates consisting of 10 g/l yeast extract, 20 g/l peptone, 20 g/l xylose, and
20 g/l agar. The undiluted fermentation medium contained 1.7 g/l filter-sterilized yeast nitrogen base (YNB)
(without amino acid and ammonium sulfate) (Difco,Detroit, Michigan) and 8.83 g/l total nitrogen
(2.27 g/l urea and 6.56 g/l peptone); pH was 5.0. During initial screening of yeasts, mixtures of pure sugars were used asthe carbon source for the fermentations. Otherwise, in most experiments, samples of wood hydrolyzate containing hexoses and pentoses in the medium were the main carbon source for the organisms employed. The
hydrolyzate samples were always filter-sterilized, whereas nitrogenous nutrients and supplements were
autoclaved and added to the medium at room temperature (25±27°C). The final pH was adjusted to 5.5±6 using sterile 1M sodium hydroxide.