Merck

Lactic acid production from xylose by engineered Saccharomyces cerevisiae without PDC or ADH deletion.

Applied microbiology and biotechnology (2015-06-06)
Timothy L Turner, Guo-Chang Zhang, Soo Rin Kim, Vijay Subramaniam, David Steffen, Christopher D Skory, Ji Yeon Jang, Byung Jo Yu, Yong-Su Jin
RESUMO

Production of lactic acid from renewable sugars has received growing attention as lactic acid can be used for making renewable and bio-based plastics. However, most prior studies have focused on production of lactic acid from glucose despite that cellulosic hydrolysates contain xylose as well as glucose. Microbial strains capable of fermenting both glucose and xylose into lactic acid are needed for sustainable and economic lactic acid production. In this study, we introduced a lactic acid-producing pathway into an engineered Saccharomyces cerevisiae capable of fermenting xylose. Specifically, ldhA from the fungi Rhizopus oryzae was overexpressed under the control of the PGK1 promoter through integration of the expression cassette in the chromosome. The resulting strain exhibited a high lactate dehydrogenase activity and produced lactic acid from glucose or xylose. Interestingly, we observed that the engineered strain exhibited substrate-dependent product formation. When the engineered yeast was cultured on glucose, the major fermentation product was ethanol while lactic acid was a minor product. In contrast, the engineered yeast produced lactic acid almost exclusively when cultured on xylose under oxygen-limited conditions. The yields of ethanol and lactic acid from glucose were 0.31 g ethanol/g glucose and 0.22 g lactic acid/g glucose, respectively. On xylose, the yields of ethanol and lactic acid were <0.01 g ethanol/g xylose and 0.69 g lactic acid/g xylose, respectively. These results demonstrate that lactic acid can be produced from xylose with a high yield by S. cerevisiae without deleting pyruvate decarboxylase, and the formation patterns of fermentations can be altered by substrates.

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Sigma-Aldrich
D-(+)-Xylose, ≥99%
Sigma-Aldrich
Calcium carbonate, ≥99.995% trace metals basis
Sigma-Aldrich
Ethyl alcohol, Pure, 190 proof, ACS spectrophotometric grade, 95.0%
Sigma-Aldrich
Calcium carbonate, BioUltra, precipitated, ≥99.0% (KT)
Sigma-Aldrich
Glycerol, BioUltra, for molecular biology, anhydrous, ≥99.5% (GC)
Sigma-Aldrich
Glycerol, BioReagent, suitable for cell culture, suitable for insect cell culture, suitable for electrophoresis, ≥99% (GC)
Sigma-Aldrich
D-(+)-Xylose, BioUltra, ≥99.0% (sum of enantiomers, HPLC)
Sigma-Aldrich
Calcium carbonate, BioReagent, suitable for insect cell culture, ≥99.0%
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Calcium carbonate, BioXtra, ≥99.0%
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Glycerol, ≥99.5%
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Glycerol, for molecular biology, ≥99.0%
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Glycerol, BioXtra, ≥99% (GC)
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D-(+)-Xylose, BioXtra, ≥99%
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DL-Lactic acid, 85 % (w/w), syrup
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Calcium carbonate, 99.999% trace metals basis
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Calcium carbonate, ACS reagent, chelometric standard, 99.95-100.05% dry basis
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Calcium carbonate, powder, ≤50 μm particle size, 98%
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Glycerol, FCC, FG
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Lactic acid solution, ACS reagent, ≥85%
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D-(+)-Xylose, ≥99%
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Ethyl alcohol, Pure, 200 proof, anhydrous, ≥99.5%
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Ethyl alcohol, Pure, 190 proof, ACS reagent, meets USP testing specifications, Excise Tax-free, Permit for use required
Sigma-Aldrich
Ethyl alcohol, Pure, 160 proof, Excise Tax-free, Permit for use required
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Lactic acid, meets USP testing specifications
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Glycerin, meets USP testing specifications
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Glycerol solution, 83.5-89.5% (T)
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Bicinchoninic acid disodium salt hydrate, ≥98% (HPLC)
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Lactic acid, natural, ≥85%
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Lactic acid, 85%, FCC
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Xylitol, ≥99%