Experimental evolution of Saccharomyces cerevisiae yeast strains for aerobic xylose fermentation

S. cerevisiae has evolved biochemical and regulatory systems to ferment glucose into ethanol at such high flux that it will do so in the presence of oxygen. This phenotype, called the Crabtree-Warburg Effect, has only been observed for glucose. In contrast, yeast strains cannot metabolize xylose aerobically without respiration, which limits biofuel production. We used a combination of directed engineering and adaptive laboratory evolution to generate S. cerevisiae strains with the abilities to ferment xylose into ethanol aerobically without the requirement for respiration. These evolved strains ferment xylose into ethanol at significantly faster rates than the parental, unevolved strain. Understanding the genetic basis of this phenotype will identify genetic modifications that could improve biofuel yield from xylose, which is a highly prevalent sugar that composes renewable plant biomass.