Víctor Guadalupe-Medina, Benjamin Metz, Bart Oud, Charlotte M. van Der Graaf, Robert Mans, Jack T. Pronk and Antonius J. A. van Maris
Glycerol formation in anaerobic S. cerevisiae cultures was recently eliminated by expressing Escherichia coli (acetylating) acetaldehyde dehydrogenase (encoded by mhpF) and simultaneously deleting the GPD1 and GPD2 genes encoding glycerol-3-phosphate dehydrogenase, thus coupling NADH reoxidation to reduction of acetate to ethanol. Gpd- strains are, however, sensitive to high sugar concentrations, which complicates industrial implementation of this metabolic engineering concept. In this study, laboratory evolution was used to improve osmotolerance of a Gpd- mhpF-expressing S. cerevisiae strain, resulting in an increase of the ethanol yield on 1M sugar from 79 % of the theoretical maximum in the Gpd+ reference strain to 92 % for the Gpd- evolved strains.