2.2. Microorganism and culture conditions
Pichia stipitis BCRC 21777 (CBS 6054) was procured from Bioresource Collection and Research Center (BCRC) in Taiwan. This yeast strain has been selected for adaptive evolution through transferred repeatedly with increasing sugar concentration. Stock cultures were maintained on YPD agar plates containing: 10 g/L of yeast extract, 20 g/L of peptone, 20 g/L of dextrose and 20 g/L of agar at 30°C for two days. Colonies from the plate were transferred by loop to a 250 mL Erlenmeyer flask containing 50 ml of YPD medium. Inoculum was grown at 30°C for 16 h with agitation of 100 rpm in an orbital shaker prior to use. The YPD medium consisted of 10 g/L of yeast extract, 20 g/L of peptone and 20 g/L of dextrose was used for inoculums.