title: Energetic benefits and rapid cellobiose fermentation by Saccharomyces cerevisiae expressing cellobiose phosphorylase and mutant cellodextrin transporters.
abstract: Anaerobic bacteria assimilate cellodextrins from plant biomass by using a phosphorolytic pathway to generate glucose intermediates for growth. The yeast Saccharomyces cerevisiae can also be engineered to ferment cellobiose to ethanol using a cellodextrin transporter and a phosphorolytic pathway. However, strains with an intracellular cellobiose phosphorylase initially fermented cellobiose slowly relative to a strain employing an intracellular β-glucosidase. Fermentations by the phosphorolytic strains were greatly improved by using cellodextrin transporters with elevated rates of cellobiose transport. Furthermore under stress conditions, these phosphorolytic strains had higher biomass and ethanol yields compared to hydrolytic strains. These observations suggest that, although cellobiose phosphorolysis has energetic advantages, phosphorolytic strains are limited by the thermodynamics of cellobiose phosphorolysis (ΔG°=+3.6kJmol(-1)). A thermodynamic "push" from the reaction immediately upstream (transport) is therefore likely to be necessary to achieve high fermentation rates and energetic benefits of phosphorolysis pathways in engineered S. cerevisiae.
authors.affiliation: Department of Food Science and Human Nutrition, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
authors.forename: Suk-Jin
authors.initials: SJ
authors.lastname: Ha
authors.forename: Jonathan M
authors.initials: JM
authors.lastname: Galazka
authors.forename: Eun
authors.initials: E
authors.lastname: Joong Oh
authors.forename: Vesna
authors.initials: V
authors.lastname: Kordić
authors.forename: Heejin
authors.initials: H
authors.lastname: Kim
authors.forename: Yong-Su
authors.initials: YS
authors.lastname: Jin
authors.forename: Jamie H D
authors.initials: JH
authors.lastname: Cate
mesh_terms: D002475:Cellobiose / Q000378:metabolism*; D002482:Cellulose / Q000031:analogs & derivatives* / Q000235:genetics / Q000378:metabolism; D003912:Dextrins / Q000235:genetics / Q000378:metabolism*; D000431:Ethanol / Q000378:metabolism*; D005285:Fermentation; D024861:Genetic Enhancement / Q000379:methods*; D005964:Glucosyltransferases / Q000235:genetics*; D016297:Mutagenesis, Site-Directed; D015202:Protein Engineering / Q000379:methods; D012441:Saccharomyces cerevisiae / Q000502:physiology*
chemical_list: D003912:Dextrins; D002475:Cellobiose; D000431:Ethanol; D002482:Cellulose; C068994:cellodextrin; D005964:Glucosyltransferases; C105024:cellodextrin phosphorylase