| Research Abstract |
Because of the need for development of alternative sources of liquid fuels, ethanol production from renewable resources has become important. Yeast are used commercially in the traditional methods for ethanol production, but ethanol-producing bacteria are now being studied because of its potential for being used in fuel ethanol production from cellulosic biomass, such as agricultural and forestry residues, and industrial wastes.
Zymomonas mobilis is a facultative anaerobic, gram-negative bacterium, and produces about 1.9mol of ethanol from 1mol of glucose, similar to industrial yeasts. We focused on the production of fuel ethanol from cellulosic wastes by using Z.mobilis. To confer the fermentation ability of cellobiose that is a hydrolysis product from cellulosic materials with an acidic treatment, β-glucosidase gene from Ruminococcus albus was introduced into Z.mobilis. The recombinant strain could ferment 2% cellobiose to ethanol with a theoretical yield without accumulation of organ
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ic acids as a metabolite. Furthermore, to confer the fermentation ability of xylose that is a hydrolysis product from hemicellulose, two operons encoding xylose assimilation enzymes, xylose isomerase and xylulokinase, and pentose phosphate pathway enzymes, transaldolase and transketolase, from Eschericha coli. The recombinant Z.mobilis could ferment 4% xylose to ethanol with the theoretical yield.
Zymobacter palmae was proposed for a new ethanol-fermenting bacterium, so its biotechnological exploitation requires genetic improvements. A method for the transformation of Z.palmae with plasmid DNA was established by using broad-host vectors. To confer the fermentation ability of cellobiose, β-glucosidase gene from R.albus was introduced into Zb.palame. The recombinant strain could ferment 2% cellobiose to ethanol with a theoretical yield without accumulation of organic acids as a metabolite. Furthermore, Zb.palmae was metabolically engineered to broaden its range of fermentable substrate to include the pentose sugar xylose. The recombinant Zb.palmae could ferment 4% xylose to ethanol with the theoretical yield. Less
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