The Construction Of Thermophilus Xylose Fermentation Engineering Yeast Strains To Produce Ethanol

Construction of Xylose co-fermentation yeast engineering strains and the optimal fermentation conditions were studied in this research. These studies have important meaning to the strains in making full use of lignocellulose biomass. S.cerevisiae G47 was gained by a great mount of screen work. This strain was characterized by growing at high temperature (45 ℃) and can ferment glucose well at this temperature. With the same substrate sugar concentration of 10%, the final ethanol concentration of the broth is 3.9% (w/w) and 2.0%(w/w) when fermenting at 41℃ and 45℃ separately. Their transform rate are 75% and 39% correspondingly.S.cerevisiae G47 and Candida shehatea 1766 which can produce ethanol by xylose-fermenting were used as the parents strains. Nine halpolids were got through halploid inducing formation and separation. The auxotrophic mutants with only one selectable marker were stable and dependable. So both of G47-2 (a) and 1766-4 (a) were induced by DES and UV in this research. It was proved that auxotrophic mutants G47-2 Lys-1(a) and 1766-4 Ura-1(a) which used as parent strains were positive mutants.We got ideal fusants between S.cerevisiae and Candida shehatea through inter-generic protoplast fusion induced by PEG and electroporation. Fusants were testified to be stable by its DNA content, the volume of cell and the stable experiment. Fusant F-71 can produce ethanol by xylose-fermenting at 45℃ and the final ethanol concentration of broth was 1.67%(v/v). Compared with parents strains, the ethanol tolerance ability of fusants were improved by 14.3%.The optimal fermentation medium composition and fermentation conditions about the fusants were studied. And the final ethanol productivity through xylose-fermenting with our fusants was 1.98%(v/v). Its transform rate was 81 %.The construction of xylose-fermenting yeasts by gene recombinant was studied briefly also.