Screening of thermotolerant yeasts for ethanol
production at high temperature
Screening of yeast strains for high ethanol production
was carried out at 40 C for three steps in YPD broth
containing 16 % glucose. Two replications were performed
in all experiments. In the first screening, ethanol
fermentation was carried out using a Durham fermentation
tube inoculated with 18–24 h culture grown on a
slant of YPD, and statically incubated for 48 h. The gas
in the Durham tube was observed, and the strains that
filled the Durham tube with gas were selected. In the secondary screening, ethanol production was carried out
in 250-ml Erlenmeyer flasks containing 100 ml of YPD
broth containing 16 % glucose. The inoculum was
prepared by transferring one loopful of 18–24 h culture
grown on a slant of YPD agar to a 125-ml Erlenmeyer
flask containing 20 ml of YPD broth. After incubation
on a rotary shaker at room temperature (27 ± 3 C) for
18–24 h, the pre-cultivated volume of inoculum was
transferred to the screening medium, to give an initial
cell concentration determined as having optical density
(OD) at 600 nm of 0.5, and then incubated on a rotary
shaker at 100 rpm and 40 C for 48 h. In the third
screening, the same medium and cultivation conditions
as in the secondary screening were used, but the
fermenting broth was analyzed for growth and ethanol
production at 6-h intervals.