COFERMENTATION OF GLUCOSE, XYLOSE, AND ARABINOSE BY MIXED CULTURES OF2 GENETICALLY-ENGINEERED ZYMOMONAS-MOBILIS STRAINS

Cofermentation of xylose and arabinose, in addition to glucose, is cri tical for complete bioconversion of lignocellulosic biomass, such as a gricultural residues and herbaceous energy crops, to ethanol. A factor ial design experiment was used to evaluate the cofermentation of gluco se, xylose, and arabinose with mixed cultures of two genetically engin eered Zymontonas mobilis strains (one ferments xylose and the other ar abinose). The pH range studied was 5.0-6.0, and the temperature range was 30-37 degrees C. The individual sugar concentrations used were 30 g/L glucose, 30 g/L xylose, and 20 g/L arabinose. The optimal cofermen tation conditions obtained by data analysis, using Design Expert softw are, were pH 5.85 and temperature 31.5 degrees C. The cofermentation p rocess yield at optimal conditions was 72.5% of theoritical maximum. T he results showed that neither the arabinose strain nor arabinose affe cted the performance of the xylose strain; however, both xylose strain and xylose had a significant effect on the performance of the arabino se strain. Although cofermentation of all three sugars is achieved by the mixed cultures, there is a preferential order of sugar utilization . Glucose is used rapidly, then xylose, followed by arabinose.