title: Metabolomic and (13)C-metabolic flux analysis of a xylose-consuming Saccharomyces cerevisiae strain expressing xylose isomerase.
abstract: Over the past two decades, significant progress has been made in the engineering of xylose-consuming Saccharomyces cerevisiae strains for production of lignocellulosic biofuels. However, the ethanol productivities achieved on xylose are still significantly lower than those observed on glucose for reasons that are not well understood. We have undertaken an analysis of central carbon metabolite pool sizes and metabolic fluxes on glucose and on xylose under aerobic and anaerobic conditions in a strain capable of rapid xylose assimilation via xylose isomerase in order to investigate factors that may limit the rate of xylose fermentation. We find that during xylose utilization the flux through the non-oxidative Pentose Phosphate Pathway (PPP) is high but the flux through the oxidative PPP is low, highlighting an advantage of the strain employed in this study. Furthermore, xylose fails to elicit the full carbon catabolite repression response that is characteristic of glucose fermentation in S. cerevisiae. We present indirect evidence that the incomplete activation of the fermentation program on xylose results in a bottleneck in lower glycolysis, leading to inefficient re-oxidation of NADH produced in glycolysis.
authors.affiliation: Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, 02139, Massachussetts.
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Wasylenko
authors.forename: Gregory
authors.initials: G
authors.lastname: Stephanopoulos
mesh_terms: D019747:Aldose-Ketose Isomerases / Q000378:metabolism*; D056804:Biofuels; D002244:Carbon / Q000378:metabolism; D000431:Ethanol / Q000378:metabolism; D060847:Metabolic Engineering; D064688:Metabolic Flux Analysis / Q000379:methods*; D053858:Metabolic Networks and Pathways; D055432:Metabolomics / Q000379:methods*; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism; D014994:Xylose / Q000032:analysis / Q000378:metabolism*
chemical_list: D056804:Biofuels; D029701:Saccharomyces cerevisiae Proteins; D000431:Ethanol; D002244:Carbon; D014994:Xylose; D019747:Aldose-Ketose Isomerases; C023298:xylose isomerase
keywords: 13C-metabolic flux analysis; Saccharomyces cerevisiae; carbon catabolite repression; cellulosic ethanol; metabolomics; xylose