Control of lactate production by Saccharomyces cerevisiae expressing a bacterial LDH gene

Potential industrial applications for lactate, such as the production of chemicals, has led to interest in producing this organic acid by metabolically engineered yeast such as Saccharomyces cerevisiae. Such microorganisms are more acid tolerant than lactic acid bacteria. This paper deals with the potential of the genetically modified S. cerevisiae strain K1-LDH (the lactate dehydrogenase gene of Lactobacillus plantarum has been integrated in the genome of the commercial wine yeast strain K1) to produce lactate and the ways to control this production. The importance of the pH control during fermentation is showed not only for preventing medium acidification but also enabling on-line lactate estimation. Fermentation behaviour of K1-LDH strain is compared to K1 (control strain): K1-LDH produces up to 40 gl(-1) of lactate mainly during the stationary phase. Influences of the main medium nutrients on the lactate production were studied by varying their initial concentration. Whilst increasing glucose concentration (S-0) until S-0 = 200 gl(-1) provides higher lactate yields, higher lactate productivity are achieved with high nitrogen concentration. Finally, continuous and resting cells culture experiments were performed and confirmed a higher lactate yield in non-growing than in growing conditions. (C) 2003 Elsevier Science Inc. All rights reserved.