The synthetic xylulose-1 phosphate pathway increases production of glycolic acid from xylose-rich sugar mixtures.
BACKGROUND
Glycolic acid (GA) is a two-carbon hydroxyacid with applications in the cosmetic, textile, and medical industry. Microbial GA production from all sugars can be achieved by engineering the natural glyoxylate shunt. The synthetic (d)-xylulose-1 phosphate (X1P) pathway provides a complementary route to produce GA from (d)-xylose. The simultaneous operation of the X1P and glyoxylate pathways increases the theoretical GA yield from xylose by 20 %, which may strongly improve GA production from hemicellulosic hydrolysates.


RESULTS
We herein describe the construction of an E. coli strain that produces GA via the glyoxylate pathway at a yield of 0.31 , 0.29 , and 0.37 g/g from glucose, xylose, or a mixture of glucose and xylose (mass ratio: 33:66 %), respectively. When the X1P pathway operates in addition to the glyoxylate pathway, the GA yields on the three substrates are, respectively, 0.39 , 0.43 , and 0.47 g/g. Upon constitutive expression of the sugar permease GalP, the GA yield of the strain which simultaneously operates the glyoxylate and X1P pathways further increases to 0.63 g/g when growing on the glucose/xylose mixture. Under these conditions, the GA yield on the xylose fraction of the sugar mixture reaches 0.75 g/g, which is the highest yield reported to date.


CONCLUSIONS
These results demonstrate that the synthetic X1P pathway has a very strong potential to improve GA production from xylose-rich hemicellulosic hydrolysates.
LISBP, CNRS, INRA, INSA, Université de Toulouse, 135 Avenue de Rangueil, 31077 Toulouse, France ; TWB, 3 rue Ariane, 31520 Ramonville-St. Agne, France.
Ceren
0000-0002-5918-142X
C
Alkim
LISBP, CNRS, INRA, INSA, Université de Toulouse, 135 Avenue de Rangueil, 31077 Toulouse, France ; TWB, 3 rue Ariane, 31520 Ramonville-St. Agne, France.
Debora
D
Trichez
LISBP, CNRS, INRA, INSA, Université de Toulouse, 135 Avenue de Rangueil, 31077 Toulouse, France ; TWB, 3 rue Ariane, 31520 Ramonville-St. Agne, France.
Yvan
Y
Cam
LISBP, CNRS, INRA, INSA, Université de Toulouse, 135 Avenue de Rangueil, 31077 Toulouse, France ; TWB, 3 rue Ariane, 31520 Ramonville-St. Agne, France.
Lucie
L
Spina
LISBP, CNRS, INRA, INSA, Université de Toulouse, 135 Avenue de Rangueil, 31077 Toulouse, France ; TWB, 3 rue Ariane, 31520 Ramonville-St. Agne, France.
Jean Marie
JM
François
LISBP, CNRS, INRA, INSA, Université de Toulouse, 135 Avenue de Rangueil, 31077 Toulouse, France ; TWB, 3 rue Ariane, 31520 Ramonville-St. Agne, France.
Thomas
T
Walther
Escherichia coli; Glucose; Glycolic acid; Synthetic pathway; Xylose
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