Xylose fermentation from lignocellulosic material using recombinant yeast cells is a promising resource for the efficient production of ethanol as a future sustainable source of energy. Experimental approaches have been emphasizing the engineering of xylose-utilizing recombinant Saccharomyces cerevisiae strains to overcome the potential bottlenecks of xylose uptake and cofactor imbalance and to minimize accumulation of xylitol. In this work, we used a computational framework on the basis of metabolic control analysis to address various issues of the xylose-glucose metabolism of Saccharomyces cerevisiae in continuous culture [1-3]. Computational simulation allowed us to investigate the limitations on the efficient production of ethanol from several existing or potential metabolic engineering strategies including the overexpression or genetic modification of xylose transporters, xylose reductase, xylulokinase, and enzymes from the pentose phosphate pathway. We find a redirection of the pyruvate intermediate flow among carboxylation, decarboxylation, and transport has significant potential in improving total utilization of hexose and pentose, and conversion of sugars into ethanol. We also find such ethanol production improvement may be achieved with a more efficient ATP molecule dissipation through maintenance demand and/or faster mitochondrial NADH turnover through the respiratory chain.

[1] Wang L, Birol I, Hatzimanikatis V. 2004. Metabolic control analysis under uncertainty: framework development and case studies. Biophys J 87: 3750-63

[2] Wang L, Hatzimanikatis V. 2006. Metabolic engineering under uncertainty - II: Analysis of yeast metabolism. Metabolic Engineering 8: 142-59

[3] Wang L, Hatzimanikatis V. 2006. Metabolic engineering under uncertainty. I: Framework development. Metabolic Engineering 8: 133-41