Screening of yeast isolates. Wild yeast strains were
selected for their tolerance to a high concentration of glucose
using YPD agar plates containing 40% dextrose.
Strains forming large colonies on plates incubated at 30o
C
for 48 hr were selected and tested further by culturing in
YPD broth containing 30, 40, or 50% dextrose at 30o
C for
24 hr with agitation (200 rpm) and compared at OD600
using a spectrophotometer (Ultrospec 2000; Pharmacia
Biotech, Upsala, Sweden). The strains were also examined
for their tolerance to high alcohol content by culturing
them on YPD agar plates containing 15 or 30%
alcohol. Those strains that could grow on the alcohol plates
were screened further by culturing them in YPD broth
containing 5~15% alcohol under the conditions described
above and then comparing the growth at OD600. The abil