Industrial strains of a polyploid, distiller's Saccharomyces cerevisiae that produces glucoamylase and α-amylase was used for the direct fermentation of raw starch to ethanol. Strains contained either Aspergillus awamori glucoamylase gene (GA1), Debaryomyces occidentalis glucoamylase gene (GAM1) or D. occidentalis α-amylase gene (AMY), singly or in combination, integrated into their chromosomes. The strain expressing both GA1 and AMY generated 10.3% (v/v) ethanol (80.9 g l(-1)) from 20% (w/v) raw corn starch after 6 days of fermentation, and decreased the raw starch content to 21% of the initial concentration.
− In this study, the physical factors for amylase production by Arthrobacter sp. were optimized using response surface methodology(RSM). Antarctic microorganism Arthrobacter sp. PAMC 27388 was obtained from the Polar and Alpine Microbial Collection(PAMC) at the Korea Polar Research Institute. This microorganism was confirmed for the excretion of amylase with Lugol`s solution. The amylase activity was after flask culture was as low as 1.66 mU/L before optimization. The physical factors including the inoculum volume, the initial culture pH, and the medium volume were chosen to be optimized for the enhanced amylase production. The calculated results using RSM indicate that the optimal physical factors were 2.49 mL inoculum volume, 6.85 pH and 42.87 mL medium volume with a predicted amylase production of 2.84 mU/L. The experimentally obtained amylase activity was 2.50 mU/L, which was a 150% increase compared to the level before optimization.
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.
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