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Applied and Environmental Microbiology, December 2001, p. 5621-5625, Vol. 67, No. 12
0099-2240/01/$04.00+0   DOI: 10.1128/AEM.67.12.5621-5625.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Efficient Homolactic Fermentation by Kluyveromyces lactis Strains Defective in Pyruvate Utilization and Transformed with the Heterologous LDH Gene†

Michele M. Bianchi,1,* Luca Brambilla,2 Francesca Protani,1 Chi-Li Liu,3 Jefferson Lievense,3 and Danilo Porro2

Department of Cell and Developmental Biology, University of Rome "La Sapienza," Rome 00185,1 and Department of Biotechnology and Biosciences, University of Milano-Bicocca, Milan 20126,2 Italy, and Tate & Lyle North America, Decatur, Illinois 625213

Received 10 May 2001/Accepted 23 September 2001

A high yield of lactic acid per gram of glucose consumed and the absence of additional metabolites in the fermentation broth are two important goals of lactic acid production by microrganisms. Both purposes have been previously approached by using a Kluyveromyces lactis yeast strain lacking the single pyruvate decarboxylase gene (KlPDC1) and transformed with the heterologous lactate dehydrogenase gene (LDH). The LDH gene was placed under the control the KlPDC1 promoter, which has allowed very high levels of lactate dehydrogenase (LDH) activity, due to the absence of autoregulation by KlPdc1p. The maximal yield obtained was 0.58 g g-1, suggesting that a large fraction of the glucose consumed was not converted into pyruvate. In a different attempt to redirect pyruvate flux toward homolactic fermentation, we used K. lactis LDH transformant strains deleted of the pyruvate dehydrogenase (PDH) E1alpha subunit gene. A great process improvement was obtained by the use of producing strains lacking both PDH and pyruvate decarboxylase activities, which showed yield levels of as high as 0.85 g g-1 (maximum theoretical yield, 1 g g-1), and with high LDH activity.

* Corresponding author. Mailing address: Department of Cell and Developmental Biology, University of Rome "La Sapienza," P.le Aldo Moro, Rome 00185, Italy. Phone: 390-649912215. Fax: 390-649912351. E-mail: Michele.Bianchi{at}uniroma1.it.

dagger This work is dedicated to Franco Tato.

Applied and Environmental Microbiology, December 2001, p. 5621-5625, Vol. 67, No. 12
0099-2240/01/$04.00+0   DOI: 10.1128/AEM.67.12.5621-5625.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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