title: Comparative metabolic network analysis of two xylose fermenting recombinant Saccharomyces cerevisiae strains.
abstract: The recombinant xylose fermenting strain Saccharomyces cerevisiae TMB3001 can grow on xylose, but the xylose utilisation rate is low. One important reason for the inefficient fermentation of xylose to ethanol is believed to be the imbalance of redox co-factors. In the present study, a metabolic flux model was constructed for two recombinant S. cerevisiae strains: TMB3001 and CPB.CR4 which in addition to xylose metabolism have a modulated redox metabolism, i.e. ammonia assimilation was shifted from being NADPH to NADH dependent by deletion of gdh1 and over-expression of GDH2. The intracellular fluxes were estimated for both strains in anaerobic continuous cultivations when the growth limiting feed consisted of glucose (2.5 g L-1) and xylose (13 g L-1). The metabolic network analysis with 13C labelled glucose showed that there was a shift in the specific xylose reductase activity towards use of NADH as co-factor rather than NADPH. This shift is beneficial for solving the redox imbalance and it can therefore partly explain the 25% increase in the ethanol yield observed for CPB.CR4. Furthermore, the analysis indicated that the glyoxylate cycle was activated in CPB.CR4.
authors.affiliation: Center for Microbial Biotechnology, BioCentrum-DTU, Building 223, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark.
authors.forename: Thomas
authors.initials: T
authors.lastname: Grotkjaer
authors.forename: Paul
authors.initials: P
authors.lastname: Christakopoulos
authors.forename: Jens
authors.initials: J
authors.lastname: Nielsen
authors.forename: Lisbeth
authors.initials: L
authors.lastname: Olsson
mesh_terms: D003198:Computer Simulation; D004734:Energy Metabolism / Q000502:physiology; D015966:Gene Expression Regulation, Fungal / Q000502:physiology; D024861:Genetic Enhancement / Q000379:methods; D008954:Models, Biological; D009097:Multienzyme Complexes / Q000502:physiology; D011995:Recombination, Genetic; D012441:Saccharomyces cerevisiae / Q000145:classification / Q000235:genetics* / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics* / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D013045:Species Specificity; D014994:Xylose / Q000378:metabolism*
chemical_list: D009097:Multienzyme Complexes; D029701:Saccharomyces cerevisiae Proteins; D014994:Xylose