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Xylose utilisation by recombinant strains of Saccharomyces cerevisiae on different carbon sources

Van Zyl W.H. ; Eliasson A. ; Hobley T. ; Hahn-Hagerdal B. (1999)


Autoselective xylose-utilising strains of Saccharomyces cerevisiae expressing the xylose reductase (XYL1) and xylitol dehydrogenase (XYL2) genes of Pichia stipitis were constructed by replacing the chromosomal FUR1 gene with a disrupted fur1::LEU2 allele. Anaerobic fermentations with 80 g l-1 D-xylose as substrate showed a twofold higher consumption of xylose in complex medium compared to defined medium. The xylose consumption rate increased a further threefold when 20 g l-1 D-glucose or raffinose was used as co-substrate together with 50 g l-1 D-xylose. Xylose consumption was higher with raffinose as co-substrate than with glucose (85% versus 71%, respectively) after 82 h fermentations. A high initial ethanol concentration and moderate levels of glycerol and acetic acid accompanied glucose as co- substrate, whereas the ethanol concentration gradually increased with raffinose as co-substrate with no glycerol and much less acetic acid formation.

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