Tuesday, April 30, 2013
Exhibit Hall
Strain background has been recognized as an important factor influencing xylose fermentation by engineered Saccharomyces cerevisiae. Previous studies suggested that industrial strains perform better than laboratory strains for ethanol production from xylose when a xylose metabolic pathway is introduced. However, most industrial strains are polyploids which are not amenable for metabolic engineering using conventional genetic tools based on auxotrophic markers. Especially, deletion of the known gene targets capable of improving xylose fermentation cannot be performed easily using polyploidy strains. To overcome these problems, we isolated haploid strains from an industrial strain (S. cerevisiae ATCC4124) and engineered the haploid strain for xylose fermentation. Specifically, HO gene disruption, sporulation, and tetrad dissection were performed to isolate haploid strains with stable mating types. After screening of the isolated haploid strains for various desirable phenotypes, a promising haploid strain was isolated and genotyped for confirmation. When the xylose metabolic pathway (XYL1, XYL2, and XYL3) from Scheffersomyces stipitis was introduced into the selected haploid, the resulting transformant was able to ferment xylose more rapidly as compared to engineered strains based on laboratory strains. We also introduced additional mutations (pho13Δ and ald6Δ) for further improving the xylose fermentation. The double deletion mutant showed a higher xylose consumption rate and accumulated less acetate as compared to the parental strain. These results demonstrate that strain background plays an important role and haploid isolation from industrial strains exhibiting high performance is a promising strategy for strain improvement.