Sunday, April 29, 2007 - 1:55 PM

Efficient fermentation of L-arabinose to ethanol by Saccharomyces cerevisiae

H. Wouter Wisselink1, M. J. Toirkens1, A. J. A. van Maris1, A.A. Winkler2, J.P. Van Dijken2, and J.T. Pronk1. (1) Industrial Microbiology, Delft University of Technology, Julianalaan 67, Delft, 2628 BC, Netherlands, (2) Bird Engineering, Westfrankelandsedijk 1, Schiedam, 3115 HG, Netherlands

Fuel ethanol production from plant-biomass hydrolysates by Saccharomyces cerevisiae is of great economic and environmental significance. Wild-type S. cerevisiae strains readily ferment the hexoses derived from these hydrolysates, such as glucose, mannose, fructose and galactose. Construction of strains that efficiently convert other potentially fermentable substrates in plant biomass hydrolysates into ethanol is a major challenge in yeast metabolic engineering. The most abundant of these compounds is the pentose sugar xylose. Recent metabolic and evolutionary engineering studies on S. cerevisiae strains that express a fungal xylose isomerase have enabled the rapid and efficient fermentation of xylose (Kuyper et al. 2005).
For cost-effective and efficient industrial ethanol production, the conversion of less predominant sugars in plant-biomass hydrolysates, such as L-arabinose, also deserves attention. Therefore, research has recently been aiming for the conversion of L-arabinose to ethanol by engineered S. cerevisiae strains. In our opinion, Boles and Becker (2003) have convincingly demonstrated that the overexpression of the bacterial L-arabinose pathway is the most promising basis for constructing L-arabinose-fermenting S. cerevisiae strains.
In this work, we present the fast and efficient anaerobic ethanolic fermentation of L-arabinose by an engineered S. cerevisiae strain. By combined expression of the complete bacterial L-arabinose utilization pathway of Lactobacillus plantarum, overexpression of enzymes from the pentose phosphate pathway, and evolutionary engineering, a strain was obtained exhibiting high rates of arabinose comsumption under anaerobic conditions. Moreover, ethanol was produced with high yields during anaerobic growth using arabinose as sole carbon source or a mixture of glucose and arabinose.