Glycolic acid production in the engineered yeasts Saccharomyces cerevisiae and Kluyveromyces lactis.
BACKGROUND
Glycolic acid is a C2 hydroxy acid that is a widely used chemical compound. It can be polymerised to produce biodegradable polymers with excellent gas barrier properties. Currently, glycolic acid is produced in a chemical process using fossil resources and toxic chemicals. Biotechnological production of glycolic acid using renewable resources is a desirable alternative.


RESULTS
The yeasts Saccharomyces cerevisiae and Kluyveromyces lactis are suitable organisms for glycolic acid production since they are acid tolerant and can grow in the presence of up to 50 g l(-1) glycolic acid. We engineered S. cerevisiae and K. lactis for glycolic acid production using the reactions of the glyoxylate cycle to produce glyoxylic acid and then reducing it to glycolic acid. The expression of a high affinity glyoxylate reductase alone already led to glycolic acid production. The production was further improved by deleting genes encoding malate synthase and the cytosolic form of isocitrate dehydrogenase. The engineered S. cerevisiae strain produced up to about 1 g l(-1) of glycolic acid in a medium containing d-xylose and ethanol. Similar modifications in K. lactis resulted in a much higher glycolic acid titer. In a bioreactor cultivation with D-xylose and ethanol up to 15 g l(-1) of glycolic acid was obtained.


CONCLUSIONS
This is the first demonstration of engineering yeast to produce glycolic acid. Prior to this work glycolic acid production through the glyoxylate cycle has only been reported in bacteria. The benefit of a yeast host is the possibility for glycolic acid production also at low pH, which was demonstrated in flask cultivations. Production of glycolic acid was first shown in S. cerevisiae. To test whether a Crabtree negative yeast would be better suited for glycolic acid production we engineered K. lactis in the same way and demonstrated it to be a better host for glycolic acid production.
VTT Technical Research Centre of Finland, Tietotie 2, Espoo FI-02044, P,O, Box 1000, VTT, Finland. outi.koivistoinen@vtt.fi.
Outi M
OM
Koivistoinen
Joosu
J
Kuivanen
Dorothee
D
Barth
Heidi
H
Turkia
Juha-Pekka
JP
Pitkänen
Merja
M
Penttilä
Peter
P
Richard
D000429:Alcohol Oxidoreductases / Q000235:genetics / Q000378:metabolism; D015966:Gene Expression Regulation, Fungal; D006016:Glycolates / Q000378:metabolism*; D007716:Kluyveromyces / Q000235:genetics / Q000378:metabolism*; D060847:Metabolic Engineering; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D023822:Tissue Engineering
D006016:Glycolates; C031149:glycolic acid; D000429:Alcohol Oxidoreductases; C020830:glyoxylate reductase