ln this study, effects of UV irradiation and 60Co-γ irradiation on fermenta-tion of xylose to ethanol by Pichia stipitis were analyzed to investigate the optimal mutagenic conditions. According to the growth curve and fermentation curve of P. stipi-tis, the optimal incubation duration and fermentation duration of P. stipitis mutant strain were 18 and 48 h, respectively. The cel concentration of original yeast liquid was 107 cel s/ml. After mutagenesis by UV irradiation and 60Co-γ irradiation, yeast liquid was incubated in 20 g/L xylose media for 48 h. According to the results, after UV irradiation for 45-75 s, transformation efficiency reached 0.3794 g/g, which was 74.39% of the theoretical value; after irradiation with 800-1 000 Gy 60Co-γ, transforma-tion efficiency reached 0.3165 g/g, which was 62.06% of the theoretical value. Therefore, both UV irradiation and 60Co-γ irradiation could improve the efficiency of xylose fermentation to ethanol by P. stipitis under appropriate conditions.
