Abstract
Saccharomyces cerevisiae was engineered to produce D-xylonate by introducing the Trichoderma reesei xyd1 gene, encoding a D-xylose dehydrogenase. D-xylonate was not toxic to S. cerevisiae, and the cells were able to export D-xylonate produced in the cytoplasm to the supernatant. Up to 3.8 g of D-xylonate per litre, at rates of 25-36 mg of D-xylonate per litre per hour, was produced. Up to 4.8 g of xylitol per litre was also produced. The yield of D-xylonate from D-xylose was approximately 0.4 g of D-xylonate per gramme of D-xylose consumed. Deletion of the aldose reductase encoding gene GRE3 in S. cerevisiae strains expressing xyd1 reduced xylitol production by 67%, increasing the yield of D-xylonate from D-xylose. However, D-xylose uptake was reduced compared to strains containing GRE3, and the total amount of D-xylonate produced was reduced. To determine whether the co-factor NADP+ was limiting for D-xylonate production the Escherichia coli transhydrogenase encoded by udhA, the Bacillus subtilis glyceraldehyde 3-phosphate dehydrogenase encoded by gapB or the S. cerevisiae glutamate dehydrogenase encoded by GDH2 was co-expressed with xyd1 in the parent and GRE3 deficient strains. Although each of these enzymes enhanced NADPH consumption on D-glucose, they did not enhance D-xylonate production, suggesting that NADP+ was not the main limitation in the current D-xylonate producing strains.
Original language | English |
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Pages (from-to) | 751-760 |
Journal | Applied Microbiology and Biotechnology |
Volume | 88 |
Issue number | 3 |
DOIs | |
Publication status | Published - 1 Oct 2010 |
MoE publication type | A1 Journal article-refereed |
Funding
Acknowledgements Eckhard Boles is thanked for the GDH2-containing plasmid YEpMSP3-T and Ritva Verho for the Δpgi1 strain (H2493). Technical assistance of Seija Rissanen, Pirjo Tähtinen and Tarja Laakso is gratefully acknowledged. This study was financially supported by the Academy of Finland through the Centre of Excellence in White Biotechnology–Green Chemistry (grant 118573) and a Research Fellowship for P. Richard. The financial support of the European Commission through the Sixth Framework Programme Integrated Project BioSynergy (038994-SES6) is also gratefully acknowledged. This publication reflects the views of the authors.
Keywords
- D-xylonic acid
- D-xylose
- Phosphoglucose isomerase
- Redox balance
- S. cerevisiae