1. Materials and methods
1.1. Anaerobic xylose fermentation
Yeast strains SR8u or SXA-R2P-E were pre-grown aerobically to
mid-log or late-log phase in oMM or YSC medium containing 2%
glucose, washed 3 times with water, and re-suspended in either
oMM or YSC medium, depending on the batch fermentation. Media
containing 4% w/v xylose (5% in Fig. 3) was inoculated with a range
of starting OD values, as indicated in the
figure panels, and then
purged with N2. Anaerobic batch fermentations were carried out in
50 mL of oMM or YSC medium in 125 mL serum bottles, closed with
butyl rubber stoppers, shaking at 220 rpm in a 30 C shaker. At the
indicated time points, 1 mL samples were removed with a syringe
and pelleted. 5 mL supernatants were analyzed by ion-exclusion
HPLC to determine xylose, xylitol, glycerol, and ethanol concentrations.