Isolation And Characters Research Of Wild Yeast Strains Which Produce Ethanol By Xylose-Fermenting

Strain No. 3 and No. 621 were two of 35 strains which isolated from nature. Their characters of morphological and fermentation of been systemic studied. Both strains have typical morphological characters of yeast, reproduction as budding and use familiar carbon resource, such as Glucose, lactose and so on. Strain No. 3 utilizes ammonium nitrogen and nitrate nitrogen. Strain No. 621 utilizes ammonium nitrogen but not nitrate nitrogen. Strain No. 3 grows at pH from 4.4 to 7.6, best of all between 6.6-7.0. Temperature ranged from 20℃-45℃, further between 28℃-30℃. Strain No. 3 grows at pH from 3.4 to 8.4, best of all between 5.2-6.4. Temperature ranged from 20℃-45℃, further between 28℃-30℃. Through 18S rDNA sequence analysis, strain No.3 is characterized as Candida intermedia and the other strain No. 621 shows highly identical 99.0% with Candida tropicalis.In conditions 28℃, 120 r/min, 72 h, strain 3 produced 6.480 g/L ethanol from 70 g/L xylose and 43.70 % theoretical production of ethanol from 30 g/L xylose. It can produce up to 21.225 g/L ethanol when incubation time prolong to 156 h from 80 g/L xylose. It also can ferment 130 g/L glucose produce 47.647 g/L ethanol and reach 76.90 % of theoretical ethanol production, respectively. Compared to CK, ethanol productivity can be improve 9.91 % when add 80 g/L xylose in three times as 30 g/L,20 g/L and 30 g/L, respectively. Glucose can be first utilized in the mixture sugar medium. Xylose-fermenting can be improve when glucose exist. Ethanol yield of mixture with 60 g/L xylose and 20 g/L glucose is 25 % more than the total yield by ferment them separate.In conditions 28℃, 120 r/min, 72 h , strain 621 produced 6.059 g/L ethanol from 90 g/L xylose and 35.08 % theoretical production of ethanol from 30 g/L xylose, and 15.593 g/L ethanol from 80 g/L xylose when incubation time prolong to 156 h. It also can ferment 110 g/L glucose produce 47.647 g/L ethanol in same conditions. Glucose can be first utilized from the mixture of xylose and glucose. Xylose-fermenting can be improve when glucose exist. Ethanol yield of mixture with 20 g/L xylose and 60 g/L glucose is 22 % more than the total yield by ferment them separate. Compared with add 80 g/L xylose in one time, ethanol productivity can be improve 11.00 % when add 80 g/L xylose in three times as 30 g/L, 20 g/L and 30 g/L, respectively. Results of Gas Chromatography analysis to the distilled products fermented from xylose, glucose or mixture of them, showed these two strains have high efficiency production of ethanol in all of them. It judged from curve direction that ethanol yield improved when aeration level in shake flask meliorate by increase of speed of shaker.Those two wild yeast strains were found to have tolerance to high osmotic pressure. Strain 3 can grow in liquid medium with up to 12 % NaCl, 6 % ethanol or 58 % glucose, while Strain 621 can grow in liquid medium with up to 16 % NaCl, or 4 % ethanol or 61 % glucose, respectively. 10 % NaCl effected the fermentation from xylose weakly.