title: Combined cell-surface display- and secretion-based strategies for production of cellulosic ethanol with Saccharomyces cerevisiae.
abstract: BACKGROUND
  Engineering Saccharomyces cerevisiae to produce heterologous cellulases is considered as a promising strategy for production of bioethanol from lignocellulose. The production of cellulase is usually pursued by one of the two strategies: displaying enzyme on the cell surface or secreting enzyme into the medium. However, to our knowledge, the combination of the two strategies in a yeast strain has not been employed.
  
  
  RESULTS
  In this study, heterologous endoglucanase (EG) and cellobiohydrolase I (CBHI) were produced in a β-glucosidase displaying S. cerevisiae strain using cell-surface display, secretion, or a combined strategy. Strains EG-D-CBHI-D and EG-S-CBHI-S (with both enzymes displayed on the cell surface or with both enzymes secreted to the surrounding medium) showed higher ethanol production (2.9 and 2.6 g/L from 10 g/L phosphoric acid swollen cellulose, respectively), than strains EG-D-CBHI-S and EG-S-CBHI-D (with EG displayed on cell surface and CBHI secreted, or vice versa). After 3-cycle repeated-batch fermentation, the cellulose degradation ability of strain EG-D-CBHI-D remained 60 % of the 1st batch, at a level that was 1.7-fold higher than that of strain EG-S-CBHI-S.
  
  
  CONCLUSIONS
  This work demonstrated that placing EG and CBHI in the same space (on the cell surface or in the medium) was favorable for amorphous cellulose-based ethanol fermentation. In addition, the cellulolytic yeast strain that produced enzymes by the cell-surface display strategy performed better in cell-recycle batch fermentation compared to strains producing enzymes via the secretion strategy.
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: Organization of Advanced Science and Technology, Kobe University, 1-1 Rokkodai, Nada-ku, Kobe, 657-8501 Japan.
authors.forename: Kentaro
authors.initials: K
authors.lastname: Inokuma
authors.affiliation: Organization of Advanced Science and Technology, Kobe University, 1-1 Rokkodai, Nada-ku, Kobe, 657-8501 Japan ; State Key Laboratory of Urban Water Resource and Environment, School of Municipal and Environmental Engineering, Harbin Institute of Technology, Harbin, 150090 People's Republic of 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 den
authors.initials: Rd
authors.lastname: Haan
authors.affiliation: Organization of Advanced Science and Technology, Kobe University, 1-1 Rokkodai, Nada-ku, Kobe, 657-8501 Japan.
authors.forename: Tomohisa
authors.initials: T
authors.lastname: Hasunuma
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: Department of Chemical Science and Engineering, Graduate School of Engineering, 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.initials: A
authors.lastname: Kondo
keywords: Cell-surface display; Cellulase; Ethanol; Saccharomyces cerevisiae; Secretion