Isolation and evolution of a novel non-saccharomyces xylose-fermenting strain for lignocellulosic bioethanol production
Conference contribution, 2014
ISOLATION AND EVOLUTION OF A NOVEL NON-SACCHAROMYCES XYLOSE-FERMENTING STRAIN FOR LIGNOCELLULOSIC BIOETHANOL PRODUCTION
Antonio D. Moreno1, Cecilia Geijer1, Elia Tomás-Pejó1,2, Lisbeth Olsson1.
1Chalmers University of Technology, Department of Chemical and Biological Engineering, Industrial Biotechnology Group, Göteborg, Sweden.
2Unit of Biotechnological Processes for Energy Production, IMDEA Energy, Móstoles (Madrid), Spain.
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The economical success of lignocellulosic bioethanol requires the fermentation of all available sugars obtained during the process. Being the major pentose sugar in lignocellulose, the fermentation of xylose is, therefore, considered essential. The fermentative yeast Saccharomyces cerevisiae is the most promising candidate for lignocellulosic bioethanol production due to its excellent glucose fermentation capability, high ethanol tolerance and resistance to inhibitors presented in lignocellulosic streams. Nevertheless, the wild type S. cerevisae is not able to ferment xylose and all of the purpose-engineered Saccharomyces strains (genetically modified microorganisms (GMO)) are still far away from an economically viable lignocellulosic ethanol production. By chance, we have discovered a non-Saccharomyces xylose-fermenting yeast (here called C5-yeast), which shows a great potential to be used for bioethanol production from lignocellulosic streams. Unlike xylose-fermenting Saccharomyces strains, the C5-yeast is not genetically modified and its use by industries can aid in finding less legislative problems when reaching the market. In the present work, the C5-yeast was isolated from a xylose-fermenting population and evolutionary engineered to enhance its fermentation abilities and robustness. During the isolation process, three different morphologies (smooth, flat and wrinkled) of the C5-yeast were found when growing the xylose-fermenting population in plates with minimal media and xylose as a sole carbon source. Among all morphologies, flat-C5-yeast showed the highest xylose consumption rates (>90% after 72 h) and the highest ethanol conversion yields (≈50% of the theoretical considering glucose and xylose) during the fermentation of wheat straw hydrolysates. The isolated flat-C5-yeast was selected for evolutionary engineering in order to enhance its sugar conversion yields and the tolerance towards the inhibitory compounds that are present in the hydrolysate. Although further characterization is needed, an evolved C5-yeast could be considered as a suitable fermentative strain for lignocellulosic bioethanol production.