Sunday, May 3, 2009 - 2:30 PM
2-04

Construction of pentose fermenting industrial Saccharomyces cerevisiae strains expressing a bacterial xylose isomerase

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

We have cloned and successfully expressed a prokaryotic xylose isomerase with high activity in the yeast Saccharomyces cerevisiae. The corresponding gene was isolated from the anaerobic bacterium Clostridium phytofermentans. The enzyme has only very limited sequence similarities to the xylose isomerases from Piromyces and Thermus thermophilus which up to now were the only xylose isomerases which could be expressed in yeast in a functional form. Activity and kinetics of the new enzyme are comparable to the Piromyces xylose isomerase. However, it is far less inhibited by xylitol, which typically is produced by yeast cells during xylose fermentations. We have expressed a codon-optimized version of the gene in industrial yeast strains. Evolutionary engineering enabled the strains to ferment xylose efficiently.

Additionally, we have also integrated genes of a bacterial arabinose pathway into the yeast strains together with an arabinose-transporter gene from Pichia stipitis. Codon-optimization of the heterologous genes considerably improved pentose fermentations. To this end, we have obtained industrial yeast strains able to produce ethanol from the main pentose sugars, xylose and arabinose, present in lignocellulosic biomass.



Web Page: cgi.server.uni-frankfurt.de/fb15/boles/start.html

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