Chemo-enzymatic production of fuel ethanol from cellulosic materials utilizing yeast expressing beta-glucosidases

Ethanol was produced in a considerably high yield by fermenting hydrolyzates from cellulosic materials by means of a recombinant laboratory yeast expressing beta-glucosidases. Tissue paper, cotton, and sawdust were hydrolyzed by two-step sulfuric acid hydrolysis to give mixtures containing glucose, cellobiose, and higher cello-oligosaccharides. After the cellulosic material was partially hydrolyzed with 80% sulfuric acid, the hydrolysis was continued with 5% sulfuric acid. Except for non-carbohydrate components, all constituents in the hydrolyzates were fermented by the yeast that was preincubated in the medium that the plasmid encoded by the beta-glucosidases gene was kept in the multiplicated yeast. A solution containing 4% hydrolyzates from paper was fermented to give as high as 1.9% maximum ethanol concentration and 70% ethanol conversion. Cotton also gave a similar result. Sawdust was converted into ethanol in approx 22% conversion. Accordingly, it was revealed that the beta-glucosidases-expressing yeast can ferment the cello-oligosaccharides obtained by hydrolysis of cellulosic materials into ethanol. In addition, a hydrolyzate containing a high glucose proportion gave a high ethanol concentration in a short time.