Fermentation of corn starch to ethanol with genetically engineered yeast

Abstract

Expression of the glucoamylase gene from Aspergillus awamori by laboratory and distiller's strains of Saccharomyces cerevisiae allowed them to ferment soluble starch. Approximately 95% of the carbohydrates in the starch were utilized. Glycerol production was significantly decreased when soluble starch was used instead of glucose. Ethanol yield on soluble starch was higher than that on glucose. The rate of starch fermentation was directly related to the level of glucoamylase activity. Strains with higher levels of glucoamylase expression fermented starch faster. The decline in starch fermentation rates toward the end of the fermentation was associated with accumulation of disaccharides and limit dextrins, poor substrates for glucoamylase. The buildup of these products in continuous fermentations inhibited glucoamylase activity and complete utilization of the starch. Under these conditions maltose-fermenting strains had a significant advantage over nonfermenting strains. The synthesis and secretion of glucoamylase showed no deleterious effects on cell growth rates, fermetation rates, and fermentation products.

Direct Production of Ethanol from Raw Corn Starch via Fermentation by Use of a Novel Surface-Engineered Yeast Strain Codisplaying Glucoamylase and α-Amylase

“…Many researchers have reported on attempts to resolve this problem by using recombinant glucoamylase-expressing yeasts with the ability to ferment starch to ethanol directly (1,3,7,9,14,16). Recombinant yeasts which coproduce glucoamylase and ␣-amylase have meanwhile been developed to further improve the efficiency of starch fermentation (2,4,6,15,21,22).…”

Hidrólise enzimática do amido de mandioca e produção de bioetanol por Saccharomyces cerevisiae CENPK2 expressando uma glicoamilase de Aspergillus awamori

“…A literatura cita o uso de fungos filamentosos selvagens ou suas glicoamilases nativas para hidrolisar amido, porém, esses microorganismos não possuem a capacidade de produzir grande quantidade de etanol. Por exemplo, Fujio et al (1984) descreveram o potencial do fungo Rhizopus koji em fermentar amido bruto de mandioca para produção de etanol alcançando uma produção de 12,1 g/L a partir de 30 g/L de amido; Flor e Hayashida (1983) relataram pela primeira vez a capacidade de glicoamilase nativa de Aspergillus awamori var; Kawachi em degradar amido bruto de milho mas os autores não informaram a quantidade de etanol produzido; Inlow et al (1988) descreveram o potencial de S. cerevisiae, expressando GA em produzir etanol, a partir da fermentação de amido solúvel de milho. Kumar, Venkateswara, Das (1995) descreveram o potencial da GA em sacarificar amido de batata; Favaro et al (2010) relataram que uma cepa de laboratório de S. cerevisiae haploide expressando a glicoamilase SgAI de Aspergillus awamori conseguiu uma produção de etanol de 5,4 g/L durante 48 horas de fermentação usando 20g/L de um amido solúvel.…”

Industrial bioprocesses: Beyond routine applications of established methodologies

“…Bioremediation (oil spills) Rise in patents (3,897/1996-5,412/1997-7,834/1998 Human genome sequence (2003) Glucose isomerase (1957) Genentech (1976) Amgen (1980) Cloned tomato (1994) Bevacizumab ( yeast host to ferment corn starch to ethanol was demonstrated by Cetus in 1988 (Inlow et al, 1988). -Trace salt and biotin feeding to improve recombinant lyzosyme production from high cell density fermentations of the methylotrophic yeast Pichia pastoris was developed by Salk in 1989 (Siegel and Brierley, 1989).…”