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Applied and Environmental Microbiology, April 1999, p. 1384-1389, Vol. 65, No. 4
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Homofermentative Production of D- or L-Lactate in Metabolically Engineered Escherichia coli RR1

Dong-Eun Chang,1,2 Heung-Chae Jung,1 Joon-Shick Rhee,2 and Jae-Gu Pan1,*

Bioprocess Engineering Division, Korea Research Institute of Bioscience and Biotechnology, Yusong, Taejon 305-600,1 and Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Yusong, Taejon 305-701,2 Korea

Received 16 September 1998/Accepted 3 January 1999

We investigated metabolic engineering of fermentation pathways in Escherichia coli for production of optically pure D- or L-lactate. Several pta mutant strains were examined, and a pta mutant of E. coli RR1 which was deficient in the phosphotransacetylase of the Pta-AckA pathway was found to metabolize glucose to D-lactate and to produce a small amount of succinate by-product under anaerobic conditions. An additional mutation in ppc made the mutant produce D-lactate like a homofermentative lactic acid bacterium. When the pta ppc double mutant was grown to higher biomass concentrations under aerobic conditions before it shifted to the anaerobic phase of D-lactate production, more than 62.2 g of D-lactate per liter was produced in 60 h, and the volumetric productivity was 1.04 g/liter/h. To examine whether the blocked acetate flux could be reoriented to a nonindigenous L-lactate pathway, an L-lactate dehydrogenase gene from Lactobacillus casei was introduced into a pta ldhA strain which lacked phosphotransacetylase and D-lactate dehydrogenase. This recombinant strain was able to metabolize glucose to L-lactate as the major fermentation product, and up to 45 g of L-lactate per liter was produced in 67 h. These results demonstrate that the central fermentation metabolism of E. coli can be reoriented to the production of D-lactate, an indigenous fermentation product, or to the production of L-lactate, a nonindigenous fermentation product.

* Corresponding author. Mailing address: Bioprocess Engineering Division, Korea Research Institute of Bioscience and Biotechnology, Yusong, Taejon 305-600, Korea. Phone: 82 42 860 4484. Fax: 82 42 860 4594. E-mail: jgpan{at}kribb4680.kribb.re.kr.

Applied and Environmental Microbiology, April 1999, p. 1384-1389, Vol. 65, No. 4
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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