DEVELOPMENT OF METABOLICALLY ENGINEERED SACCHAROMYCES-CEREVISIAE CELLS FOR THE PRODUCTION OF LACTIC-ACID

Interesting challenges from metabolically engineered Saccharomyces cer evisiae cells arise from the opportunity to obtain yeast strains usefu l for the production of chemical(s). In this paper, we describe the ac cumulation of lactic acid in the culture medium of growing, engineered yeast cells expressing a mammalian lactate dehydrogenase gene (LDH-A) . High and reproducible productions (20 g/L) and productivities (up to 11 g/L/h) of lactic acid have been, obtained by modulating the physio logical growth conditions. Since yeast cells are acid tolerant and sur vive at very low pH values, the production of lactate Can be avoided. In perspective; the approaches described could be useful for the produ ction of lactic acid, outflanking the problems related to the synthesi s from bacteria cells. In fact, during industrial productions, there i s an inhibitory effect on the metabolic activities of the growing bact eria (i.e., Lactobacillus spp.) caused by the acid produced and by the low pH value. Thus, strategies to prevent the lowering of pH are conv entional operations. These processes allow the production of lactate(s ) and require the purification of the acid from its salt. The biotechn ological implications of this study are also discussed.