Abstract
The important platform chemicals ethylene glycol and glycolic acid were produced via the oxidative D-xylose pathway in the yeast Saccharomyces cerevisiae. The expression of genes encoding D-xylose dehydrogenase (XylB) and D-xylonate dehydratase (XylD) from Caulobacter crescentus and YagE or YjhH aldolase and aldehyde dehydrogenase AldA from Escherichia coli enabled glycolic acid production from D-xylose up to 150 mg/L. In strains expressing only xylB and xylD, 29 mg/L 2-keto-3-deoxyxylonic acid [(S)-4,5-dihydroxy-2-oxopentanoic acid] (2K3DXA) was produced and D-xylonic acid accumulated to ca. 9 g/L. A significant amount of D-xylonic acid (ca. 14%) was converted to 3-deoxypentonic acid (3DPA), and also, 3,4-dihydroxybutyric acid was formed. 2K3DXA was further converted to glycolaldehyde when genes encoding by either YagE or YjhH aldolase from E. coli were expressed. Reduction of glycolaldehyde to ethylene glycol by an endogenous aldo-keto reductase activity resulted further in accumulation of ethylene glycol of 14 mg/L. The possibility of simultaneous production of lactic and glycolic acids was evaluated by expression of gene encoding lactate dehydrogenase ldhL from Lactobacillus helveticus together with aldA. Interestingly, this increased the accumulation of glycolic acid to 1 g/L. The D-xylonate dehydratase activity in yeast was notably low, possibly due to inefficient Fe–S cluster synthesis in the yeast cytosol, and leading to D-xylonic acid accumulation. The dehydratase activity was significantly improved by targeting its expression to mitochondria or by altering the Fe–S cluster metabolism of the cells with FRA2 deletion.
Original language | English |
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Pages (from-to) | 8151-8163 |
Journal | Applied Microbiology and Biotechnology |
Volume | 101 |
Issue number | 22 |
DOIs | |
Publication status | Published - 1 Nov 2017 |
MoE publication type | A1 Journal article-refereed |
Funding
This study was financially supported by the Academy of Finland through the Centre of Excellence in White Biotechnology—Green Chemistry (grant 118573) and the Pentoval project (grant 129174) and by the Finnish Funding Agency for Innovation (TEKES) (Living Factories project 562/31/2014).
Keywords
- D-Xylonic acid
- D-Xylose
- ethylene glycol
- glycolic acid
- saccharomyces cerevisiae