Sunday, April 29, 2007

Optimization of arabinose conversion in yeast strains

Beate Wiedemann, Institute of Molecular Biosciences, Goethe-University Frankfurt/Main, Max-von-Laue-Str.9, Frankfurt/Main, Germany and Eckhard Boles, Institute of Molecular Biosciences, Goethe-University Frankfurt, Max-von-Laue-Str. 9, Frankfurt, 60438, Germany.

Bioethanol produced by microbial fermentations is an excellent alternative to fossil fuels and plant biomass, particularly when accruing as waste product, is an attractive feedstock. In industrial processes the yeast Saccharomyces cerevisiae is commonly used for ethanol production. Hydrolysates of such lignocellulosic materials contain hexose and pentose sugars. S. cerevisiae is able to produce high ethanol yields from hexose sugars but lacks the ability to ferment pentose sugars. To increase ecological and economical revenue it is necessary to expand the substrate range and thus to increase ethanol yields produced by yeast. D-xylose is the most abundant hemicellulosic sugar. Nevertheless, corn fiber and many herbaceous crops contain significant amounts of L-arabinose. Furthermore, processing of crops such as soybeans produce large amounts of L-arabinose as waste. Different strategies employing genetic engineering have been used to enable pentose fermentation by S. cerevisiae. In our group arabinose fermentation in S. cerevisiae has been achieved by expressing a bacterial pathway for L-arabinose utilization. This recombinant yeast strain is able to convert L-arabinose into ethanol. The strain has now been considerably improved by genetic and physiological means to further increase ethanol production from L-arabinose. We will present results regarding this optimization.