title: Improved ethanol production by engineered Saccharomyces cerevisiae expressing a mutated cellobiose transporter during simultaneous saccharification and fermentation.
abstract: Although simultaneous saccharification and fermentation (SSF) of cellulosic biomass can offer efficient hydrolysis of cellulose through alleviating feed-back inhibition of cellulases by glucose, supplementation of β-glucosidase is necessary because most fermenting microorganisms cannot utilize cellobiose. Previously, we observed that SSF of cellulose by an engineered Saccharomyces cerevisiae expressing a cellobiose transporter (CDT-1) and an intracellular β-glucosidase (GH1-1) without β-glucosidase could not be performed as efficiently as the traditional SSF with extracellular β-glucosidase. However, we improved the ethanol production from SSF of cellulose by employing a further engineered S. cerevisiae expressing a mutant cellobiose transporter [CDT-1 (F213L) exhibiting higher VMAXthan CDT-1] and GH1-1 in this study. Furthermore, limitation of cellobiose formation by reducing the amounts of cellulases mixture in SSF could lead the further engineered strain to produce ethanol considerably better than the parental strain with β-glucosidase. Probably, better production of ethanol by the further engineered strain seemed to be due to a higher affinity to cellobiose, which might be attributed to not only 2-times lower Monod constant (KS) for cellobiose than KSof the parental strain for glucose but also 5-times lower KSthan Michaelis-Menten constant (KM) of the extracellular β-glucosidase for glucose. Our results suggest that modification of the cellobiose transporter in the engineered yeast to transport lower level of cellobiose enables a more efficient SSF for producing ethanol from cellulose.
authors.affiliation: Department of Food Science and Human Nutrition, and Institute for Genomic Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, United States; Department of Bioenergy Science and Technology, Chonnam National University, Gwangju 500-757, South Korea.
authors.forename: Won-Heong
authors.initials: WH
authors.lastname: Lee
authors.affiliation: Department of Food Science and Human Nutrition, and Institute for Genomic Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, United States. Electronic address: ysjin@illinois.edu.
authors.forename: Yong-Su
authors.initials: YS
authors.lastname: Jin
mesh_terms: D002475:Cellobiose / Q000235:genetics / Q000378:metabolism; D000431:Ethanol / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000096:biosynthesis / Q000235:genetics; D030781:Organisms, Genetically Modified / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000096:biosynthesis / Q000235:genetics; D001617:beta-Glucosidase / Q000096:biosynthesis / Q000235:genetics
chemical_list: D026901:Membrane Transport Proteins; D029701:Saccharomyces cerevisiae Proteins; D002475:Cellobiose; D000431:Ethanol; D001617:beta-Glucosidase
keywords: Cellobiose transporter; Cellulosic ethanol; Engineered Saccharomyces cerevisiae; Intracellular β-glucosidase; Simultaneous saccharification and fermentation