Raw starch fermentation to ethanol by an industrial distiller’s yeast strain of Saccharomyces cerevisiae expressing glucoamylase and α-amylase genes

Abstract

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.

Construction of Amylolytic Industrial Strains of Saccharomyces cerevisiae for Improved Ethanol Production from Raw Starch

“…ATCC 9763/YIpδAGSAδ/YIpSA2rD, which showed 1.2-times higher AMY activity than the parental strain, generated 7.9% (v/v) ethanol after 3 days of fermentation. This value was about 1.3-times higher than the ethanol concentration produced by the parental strain during the same period [6.2% (v/v)] (Kim et al, 2011). In contrast, the ability of ATCC 9763/YIpδAGSAδ/YIpBA2rD to directly ferment ethanol from raw starch, which co-produces GA1, AMY, and Amy, was not distinctly different from that of the parental strain.…”

“…The activities of α-amylase and glucoamylase improved with increasing copy numbers via rDNA-integration (Kim et al, 2010), reaching 6.95 U/ml and 1.08 U/ml, respectively in ATCC 9763/YIpδAGSAδ/YIpSA2rD and ATCC 9763/YIpδ AGSAδ/YIpAG2rD. These values were 1.2-times and 1.9-times higher than the respective activities of the parental strain (Kim et al, 2011). The additional multicopy rDNA-integration of the GA1 or AMY genes can be correlated with the high-level expression of the corresponding genes (Nieto et al, 1999;Choi et al, 2002).…”

“…For industrial-scale fermentation, ethanol productivity from raw starch depends on the improvement of amylase activities (Yamada et al, 2009(Yamada et al, , 2010. Manipulation of S. cerevisiae to expresses high RSDE activities, via δ-integration and rDNA-integration of the RSDE genes, can be useful for the improvement of ethanol productivity from raw starch (Kim et al, 2011;Yamada et al, 2012). We recently constructed δ -integrative and rDNA-integrative vectors to allow for the multiple integration of amylase genes into the chromosomes of industrial strains (Ghang et al, 2007;Kim et al, 2010).…”

“…Bacillus amyloliquefaciens ATCC 23842 was the source of the Amy gene (Gangadharan et al, 2010). ATCC 9763/YIpδAGSAδ was constructed from the industrial strain of S. cerevisiae ATCC 9763 (Kim et al, 2011) and was used as the host for the yeast transformation experiment. Plasmids YIpδAURAGδ and YIpδAURSAδ (Ghang et al, 2007) were used as sources of GA1 and AMY genes, respectively.…”

“…The recipient parental yeast strain for introducing the linearized 18S rDNA cassettes was ATCC 9763/YIpδAGSAδ, which produces ethanol from raw starch due to its relatively strong raw starch-degrading glucoamylase activity (Kim et al, 2011). To examine the effect of rDNA-integration on amylase activities, α-amylase and glucoamylase activities were measured in the culture supernatants from transformants grown in YPS media.…”