3. Results and discussion
3.1. Fermentation performance in mixed sugars
In this study, we sought to evaluate the performance of an efficient
xylose-utilizing strain harboring a xylose isomerase pathway
during the fermentation of the lignocellulosic hydrolysate. To this
end, we initially investigated the co-fermentation performance of
mixed sugars using the recombinant S. cerevisiae strain SXA-R2PE,
of which the ethanol fermentation performance was among
the highest ever reported when xylose was used as a single carbon
source. Specifically, anaerobic fermentation was carried out in a
synthetic medium supplied with 20 g/L of glucose (Fig. 1a), 20
g/L of xylose (Fig. 1b), mixed sugars of 10 g/L glucose and 10 g/L
of xylose (Fig. 1c) and of 20 g/L glucose and 20 g/L xylose
(Fig. 1d). Nearly all of the xylose was utilized within 48 h
(Fig. 1b–d), while the glucose was rapidly consumed within 2 h
(Fig. 1a). In the presence of glucose, the initial xylose consumption
rate (0.6 g/L/h; 0–12 h; Fig. 1d) was lower than the rate when only
xylose was used (0.95 g/L/h; 0–12 h; Fig. 1b). However, the overall
xylose consumption rates were similar for both fermentations with
only xylose (0.40 g/L/h; 0–48 h; Fig. 1b) and with the mixed sugars
(0.38 g/L/h; 0–48 h; Fig. 1d).