Improvement of tolerance of Saccharomyces cerevisiae to hot-compressed water-treated cellulose by expression of ADH1.
Hot-compressed water treatment of cellulose and hemicellulose for subsequent bioethanol production is a novel, economically feasible, and nonhazardous method for recovering sugars. However, the hot-compressed water-treated cellulose and hemicellulose inhibit subsequent ethanol fermentation by the yeast Saccharomyces cerevisiae. To overcome this problem, we engineered a yeast strain with improved tolerance to hot-compressed water-treated cellulose. We first determined that glycolaldehyde has a greater inhibitory effect than 5-HMF and furfural and a combinational effect with them. On the basis of the hypothesis that the reduction of glycolaldehyde to ethylene glycol should detoxify glycolaldehyde, we developed a strain overexpressing the alcohol dehydrogenase gene ADH1. The ADH1-overexpressing strain exhibits an improved fermentation profile in a glycolaldehyde-containing medium. The conversion ratio of glycolaldehyde to ethylene glycol is 30 ± 1.9% when the control strain is used; this ratio increases to 77 ± 3.6% in the case of the ADH1-overexpressing strain. A glycolaldehyde treatment and the overexpression of ADH1 cause changes in the fermentation products so as to balance the metabolic carbon flux and the redox status. Finally, the ADH1-overexpressing strain shows a statistically significantly improved fermentation profile in a hot-compressed water-treated cellulose-containing medium. The conversion ratio of glycolaldehyde to ethylene glycol is 33 ± 0.85% when the control strain is used but increases to 72 ± 1.7% in the case of the ADH1-overexpressing strain. These results show that the reduction of glycolaldehyde to ethylene glycol is a promising strategy to decrease the toxicity of hot-compressed water-treated cellulose. This is the first report on the improvement of yeast tolerance to hot-compressed water-treated cellulose and glycolaldehyde.
Department of Environmental Sciences, Saga University, 1 Honjo-cho, Saga 840-8502, Japan.
Lahiru N
LN
Jayakody
Kenta
K
Horie
Nobuyuki
N
Hayashi
Hiroshi
H
Kitagaki
D000426:Alcohol Dehydrogenase / Q000235:genetics / Q000378:metabolism*; D002482:Cellulose / Q000737:chemistry / Q000378:metabolism*; D000431:Ethanol / Q000378:metabolism; D015870:Gene Expression; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*
D029701:Saccharomyces cerevisiae Proteins; D000431:Ethanol; D002482:Cellulose; C516801:ADH1 protein, S cerevisiae; D000426:Alcohol Dehydrogenase