Results and discussion
Screening of xylose-fermenting yeast
We obtained 72 yeast strains able to ferment xylose
from the approximate 100 natural samples collected.
The ethanol production ability of each isolated strain
was determined using a rich medium with YPX medium
containing 4% xylose. Among the isolated strains, 16
strains produced a significant amount of ethanol from
xylose. To examine the fermentability of xylose, the time
courses of ethanol concentration and xylose consumption
from YPX medium at different temperatures were
monitored by HPLC. We observed that one yeast strain,
strain ATY839 (which was isolated from soil in Kyoto
University) exhibited high xylose fermentability (data not
shown).
Temperature characterization of growth and ethanol
production in strain ATY839
To investigate the growth and ethanol production of
strain ATY839 at different temperatures, glucose or xylose
were fermented at 35, 36, 38, and 39°C. The time
course analyses of cell growth in SG and SX media are
shown in Figure 1a and Figure 1b, respectively. Strain
ATY839 was able to grow even at 39°C in any of the carbon
sources tested.