Metabolic engineering of Corynebacterium glutamicum for hyperproduction of polymer-grade l- and d-lactic acid
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Strain development is critical for microbial production of bio-based chemicals. The stereo-complex form of polylactic acid, a complex of poly-l- and poly-d-lactic acid, is a promising polymer candidate due to its high thermotolerance. Here, we developed Corynebacterium glutamicum strains producing high amounts of l- and d-lactic acid through intensive metabolic engineering. Chromosomal overexpression of genes encoding the glycolytic enzymes, glucokinase, glyceraldehyde-3-phosphate dehydrogenase, phosphofructokinase, triosephosphate isomerase, and enolase, increased l- and d-lactic acid concentration by 146% and 56%, respectively. Chromosomal integration of two genes involved in the Entner–Doudoroff pathway (6-phosphogluconate dehydratase and 2-dehydro-3-deoxyphosphogluconate aldolase), together with a gene encoding glucose-6-phosphate dehydrogenase from Zymomonas mobilis, to bypass the carbon flow from glucose, further increased l- and d-lactic acid concentration by 11% and 44%, respectively. Finally, additional chromosomal overexpression of a gene encoding NADH dehydrogenase to modulate the redox balance resulted in the production of 212 g/L l-lactic acid with a 97.9% yield and 264 g/L d-lactic acid with a 95.0% yield. The optical purity of both l- and d-lactic acid was 99.9%. Because the constructed metabolically engineered strains were devoid of plasmids and antibiotic resistance genes and were cultivated in mineral salts medium, these strains could contribute to the cost-effective production of the stereo-complex form of polylactic acid in practical scale.
KeywordsCorynebacterium glutamicum Metabolic engineering Lactic acid Glycolytic enzymes Entner–Doudoroff pathway
This work was supported by a grant from the New Energy and Industrial Technology Development Organization (NEDO).
Compliance with ethical standards
This article does not contain any studies with human participants or animals performed by any of the authors.
Conflict of interest
The authors declare that they have no conflict of interest.
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