title: Xylose isomerase overexpression along with engineering of the pentose phosphate pathway and evolutionary engineering enable rapid xylose utilization and ethanol production by Saccharomyces cerevisiae.
abstract: Xylose is the main pentose and second most abundant sugar in lignocellulosic feedstocks. To improve xylose utilization, necessary for the cost-effective bioconversion of lignocellulose, several metabolic engineering approaches have been employed in the yeast Saccharomyces cerevisiae. In this study, we describe the rational metabolic engineering of a S. cerevisiae strain, including overexpression of the Piromyces xylose isomerase gene (XYLA), Pichia stipitis xylulose kinase (XYL3) and genes of the non-oxidative pentose phosphate pathway (PPP). This engineered strain (H131-A3) was used to initialize a three-stage process of evolutionary engineering, through first aerobic and anaerobic sequential batch cultivation followed by growth in a xylose-limited chemostat. The evolved strain H131-A3-AL(CS) displayed significantly increased anaerobic growth rate (0.203±0.006 h⁻¹) and xylose consumption rate (1.866 g g⁻¹ h⁻¹) along with high ethanol conversion yield (0.41 g/g). These figures exceed by a significant margin any other performance metrics on xylose utilization and ethanol production by S. cerevisiae reported to-date. Further inverse metabolic engineering based on functional complementation suggested that efficient xylose assimilation is attributed, in part, to the elevated expression level of xylose isomerase, which was accomplished through the multiple-copy integration of XYLA in the chromosome of the evolved strain.
authors.affiliation: Department of Chemical Engineering, Massachusetts Institute of Technology, Room 56-469, 77 Massachusetts Avenue, Cambridge, MA 02139, USA.
authors.forename: Hang
authors.initials: H
authors.lastname: Zhou
authors.forename: Jing-Sheng
authors.initials: JS
authors.lastname: Cheng
authors.forename: Benjamin L
authors.initials: BL
authors.lastname: Wang
authors.forename: Gerald R
authors.initials: GR
authors.lastname: Fink
authors.forename: Gregory
authors.initials: G
authors.lastname: Stephanopoulos
mesh_terms: D019747:Aldose-Ketose Isomerases / Q000235:genetics / Q000378:metabolism*; D019020:Directed Molecular Evolution / Q000379:methods; D000431:Ethanol / Q000302:isolation & purification / Q000378:metabolism*; D024861:Genetic Enhancement / Q000379:methods; D010427:Pentose Phosphate Pathway / Q000235:genetics*; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000235:genetics; D010843:Pichia / Q000502:physiology; D020089:Piromyces / Q000502:physiology; D015202:Protein Engineering / Q000379:methods*; D012441:Saccharomyces cerevisiae / Q000502:physiology*; D015854:Up-Regulation / Q000502:physiology; D014994:Xylose / Q000378:metabolism*
chemical_list: D000431:Ethanol; D014994:Xylose; D017853:Phosphotransferases (Alcohol Group Acceptor); C032700:xylulokinase; D019747:Aldose-Ketose Isomerases; C023298:xylose isomerase