Metabolic engineering of ammonium assimilation in xylose-fermenting Saccharomyces cerevisiae improves ethanol production.
Cofactor imbalance impedes xylose assimilation in Saccharomyces cerevisiae that has been metabolically engineered for xylose utilization. To improve cofactor use, we modified ammonia assimilation in recombinant S. cerevisiae by deleting GDH1, which encodes an NADPH-dependent glutamate dehydrogenase, and by overexpressing either GDH2, which encodes an NADH-dependent glutamate dehydrogenase, or GLT1 and GLN1, which encode the GS-GOGAT complex. Overexpression of GDH2 increased ethanol yield from 0.43 to 0.51 mol of carbon (Cmol) Cmol(-1), mainly by reducing xylitol excretion by 44%. Overexpression of the GS-GOGAT complex did not improve conversion of xylose to ethanol during batch cultivation, but it increased ethanol yield by 16% in carbon-limited continuous cultivation at a low dilution rate.
Roca
Christophe
C
Center for Process Biotechnology, BioCentrum-DTU, Technical University of Denmark, 2800 Kongens Lyngby, Denmark.
Nielsen
Jens
J
Olsson
Lisbeth
L
D000641:Ammonia / Q000378:metabolism*; D000431:Ethanol / Q000378:metabolism*; D005285:Fermentation; D005818:Genetic Engineering; D005969:Glutamate Dehydrogenase / Q000235:genetics; D005970:Glutamate Synthase / Q000235:genetics; D005974:Glutamate-Ammonia Ligase / Q000235:genetics; D009243:NAD / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D014994:Xylose / Q000378:metabolism*
D009243:NAD; D000431:Ethanol; D000641:Ammonia; D014994:Xylose; D005970:Glutamate Synthase; D005969:Glutamate Dehydrogenase; C081173:glutamine synthetase I; D005974:Glutamate-Ammonia Ligase