Construction and analysis of high-ethanol-producing fusants with co-fermentation ability through protoplast fusion and double labeling technology.

Double labeling of resistance markers and report genes can be used to breed engineered Saccharomyces cerevisiae strains that can assimilate xylose and glucose as a mixed carbon source for ethanol fermentation and increased ethanol production. In this study Saccharomyces cerevisiae W5 and Candida shehatae 20335 were used as parent strains to conduct protoplast fusion and the resulting fusants were screened by double labeling. High performance liquid chromatography (HPLC) was used to assess the ethanol yield following the fermentation of xylose and glucose, as both single and mixed carbon sources, by the fusants. Interestingly, one fusant (ZLYRHZ7) was demonstrated to have an excellent fermentation performance, with an ethanol yield using the mixed carbon source of 0.424 g g-1, which compares with 0.240 g g-1 (W5) and 0.353 g g-1 (20335) for the parent strains. This indicates an improvement in the ethanol yield of 43.4% and 16.7%, respectively.