To contruct amylolytic industrial strains of Saccharomyces cerevisiae which produce ethanol efficiently from raw starch, the Bacillus amyloliquefaciens α-amylase genes (Amy) or Aspergillus awamori glucoamylase genes (GA1) was separately introduced into the ribosomal DNA loci in the chromosomes of the raw starch fermenting-parental strain (ATCC 9763/YIpδAGSAδ), using double 18S rDNA-integration system. Ethanol production after 3 days of fermentation by the strain that produced ethanol most efficiently from raw starch (ATCC 9763/YIpδAGSAδ /YIpAG2rD) among the transformant strains was 1.5-times higher than that by the parental strain. This new strain generated 9.2% (v/v) ethanol (72 g/L) from 20% (w/v) raw corn starch and consumed 75% of the raw starch content during the same period.
To improve antioxidant glutathione (GSH) content and saccharification ability in sake yeasts of Saccharomyces cerevisiae, the γ-glutamylcysteine synthetase gene (GSH1 ) from S. cerevisiae, glucoamylase gene (GAM1 ) and α-amylase gene (AMY ) from Debaryomyces occidentalis were co-expressed in sake yeasts for manufacturing a refreshing alcoholic beverage abundant in GSH from rice starch. The extracellular GSH content of the recombinant sake yeasts increased 1.5-fold relative to the parental wide-type strain. The saccharification ability by glucoamylase of the new yeast strain expressing both GAM1 and AMY genes was 2-fold higher than that of the yeast strain expressing only GAM1 gene when grown in the culture medium containing 2% (w/v) rice starch. It generated 11% (v/v) ethanol from 20% (w/v) rice starch and consumed up to 90% of the starch content after 7 days of fermentation.
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