title: Enhanced direct ethanol production by cofactor optimization of cell surface-displayed xylose isomerase in yeast.
abstract: Xylose isomerase (XylC) from Clostridium cellulovorans can simultaneously perform isomerization and fermentation of d-xylose, the main component of lignocellulosic biomass, and is an attractive candidate enzyme. In this study, we optimized a specified metal cation in a previously established Saccharomyces cerevisiae strain displaying XylC. We investigated the effect of each metal cation on the catalytic function of the XylC-displaying S. cerevisiae. Results showed that the divalent cobalt cations (Co2+) especially enhanced the activity by 46-fold. Co2+also contributed to d-xylose fermentation, which resulted in improving ethanol yields and xylose consumption rates by 6.0- and 2.7-fold, respectively. Utility of the extracellular xylose isomerization system was exhibited in the presence of mixed sugar. XylC-displaying yeast showed the faster d-xylose uptake than the yeast producing XI intracellularly. Furthermore, direct xylan saccharification and fermentation was performed by unique yeast co-culture system. A xylan-degrading yeast strain was established by displaying two kinds of xylanases; endo-1,4-β-xylanase (Xyn11B) from Saccharophagus degradans, and β-xylosidase (XlnD) from Aspergillus niger. The yeast co-culture system enabled fine-tuning of the initial ratios of the displayed enzymes (Xyn11B:XlnD:XylC) by adjusting the inoculation ratios of Xylanases (Xyn11B and XlnD)-displaying yeast and XylC-displaying yeast. When the enzymes were inoculated at the ratio of 1:1:2 (1.39 × 1013: 1.39 × 1013: 2.78 × 1013molecules), 6.0 g/L ethanol was produced from xylan. Thus, the cofactor optimization and the yeast co-culture system developed in this study could expand the prospect of biofuels production from lignocellulosic biomass. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 33:1068-1076, 2017.
authors.affiliation: Graduate School of Advanced Integrated Studies in Human Survivability, Kyoto University, Sakyo-ku, Kyoto, 606-8306, Japan.|Div. of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto, 606-8502, Japan.|CREST, JST, Sakyo-ku, Kyoto, 606-8502, Japan.
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Sasaki
authors.affiliation: Div. of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto, 606-8502, Japan.|CREST, JST, Sakyo-ku, Kyoto, 606-8502, Japan.|Japan Society for the Promotion of Science, Sakyo-ku, Kyoto, 606-8502, Japan.
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Takagi
authors.affiliation: Div. of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto, 606-8502, Japan.|CREST, JST, Sakyo-ku, Kyoto, 606-8502, Japan.
authors.forename: Keisuke
authors.initials: K
authors.lastname: Motone
authors.affiliation: Div. of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto, 606-8502, Japan.|CREST, JST, Sakyo-ku, Kyoto, 606-8502, Japan.
authors.forename: Kouichi
authors.initials: K
authors.lastname: Kuroda
authors.affiliation: Div. of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto, 606-8502, Japan.|CREST, JST, Sakyo-ku, Kyoto, 606-8502, Japan.
authors.forename: Mitsuyoshi
authors.identifier: http://orcid.org/0000-0003-2268-2391
authors.initials: M
authors.lastname: Ueda
mesh_terms: D019747:Aldose-Ketose Isomerases / Q000378:metabolism*; D002462:Cell Membrane / Q000201:enzymology* / Q000378:metabolism; D018920:Coculture Techniques; D000431:Ethanol / Q000737:chemistry / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000201:enzymology* / Q000378:metabolism*
chemical_list: D000431:Ethanol; D019747:Aldose-Ketose Isomerases; C023298:xylose isomerase
keywords: Saccharomyces cerevisiae; bioethanol; metal cation; xylan; xylose isomerase