title: Improvement of ethanol production from crystalline cellulose via optimizing cellulase ratios in cellulolytic Saccharomyces cerevisiae.
abstract: Crystalline cellulose is one of the major contributors to the recalcitrance of lignocellulose to degradation, necessitating high dosages of cellulase to digest, thereby impeding the economic feasibility of cellulosic biofuels. Several recombinant cellulolytic yeast strains have been developed to reduce the cost of enzyme addition, but few of these strains are able to efficiently degrade crystalline cellulose due to their low cellulolytic activities. Here, by combining the cellulase ratio optimization with a novel screening strategy, we successfully improved the cellulolytic activity of a Saccharomyces cerevisiae strain displaying four different synergistic cellulases on the cell surface. The optimized strain exhibited an ethanol yield from Avicel of 57% of the theoretical maximum, and a 60% increase of ethanol titer from rice straw. To our knowledge, this work is the first optimization of the degradation of crystalline cellulose by tuning the cellulase ratio in a cellulase cell-surface display system. This work provides key insights in engineering the cellulase cocktail in a consolidated bioprocessing yeast strain. Biotechnol. Bioeng. 2017;114: 1201-1207. © 2017 Wiley Periodicals, Inc.
authors.affiliation: Department of Chemical Science and Engineering, Graduate School of Engineering, Kobe University, 1-1 Rokkodai, Nada-ku, Kobe 657-8501, Japan.
authors.forename: Zhuo
authors.initials: Z
authors.lastname: Liu
authors.affiliation: Graduate School of Science, Technology and Innovation, Kobe University, 1-1 Rokkodai, Nada-ku, Kobe 657-8501, Japan.
authors.forename: Kentaro
authors.initials: K
authors.lastname: Inokuma
authors.affiliation: State Key Laboratory of Urban Water Resource and Environment, School of Municipal and Environmental Engineering, Harbin Institute of Technology, Harbin 150090, PR China.
authors.forename: Shih-Hsin
authors.initials: SH
authors.lastname: Ho
authors.affiliation: Department of Biotechnology, University of the Western Cape, Bellville 7530, South Africa.
authors.forename: Riaan
authors.initials: R
authors.lastname: den Haan
authors.affiliation: Department of Microbiology, University of Stellenbosch, Stellenbosch 7600, South Africa.
authors.forename: Willem H
authors.initials: WH
authors.lastname: van Zyl
authors.affiliation: Graduate School of Science, Technology and Innovation, Kobe University, 1-1 Rokkodai, Nada-ku, Kobe 657-8501, Japan.
authors.forename: Tomohisa
authors.initials: T
authors.lastname: Hasunuma
authors.affiliation: Department of Chemical Science and Engineering, Graduate School of Engineering, Kobe University, 1-1 Rokkodai, Nada-ku, Kobe 657-8501, Japan.|Graduate School of Science, Technology and Innovation, Kobe University, 1-1 Rokkodai, Nada-ku, Kobe 657-8501, Japan.|Biomass Engineering Program, RIKEN, 1-7-22 Suehiro-cho, Tsurumi-ku, Yokohama, Kanagawa, 230-0045, Japan.
authors.forename: Akihiko
authors.identifier: 0000-0003-1527-5288
authors.initials: A
authors.lastname: Kondo
mesh_terms: D002480:Cellulase / Q000502:physiology*; D002482:Cellulose / Q000737:chemistry / Q000378:metabolism*; D003460:Crystallization; D004789:Enzyme Activation; D000431:Ethanol / Q000302:isolation & purification / Q000378:metabolism*; D024861:Genetic Enhancement / Q000379:methods*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000145:classification* / Q000502:physiology*; D013045:Species Specificity; D013379:Substrate Specificity
chemical_list: D011994:Recombinant Proteins; D000431:Ethanol; D002482:Cellulose; D002480:Cellulase
keywords: Saccharomyces cerevisiae; cell-surface display; cellulase ratio; cellulosic ethanol; crystalline cellulose