In ethanol fermentation, pyruvic acid is converted into acetaldehyde and CO2 by pyruvate decarboxylase (PDC; EC4.1.1.1), and the acetaldehyde is subsequently converted into ethanol by alcohol dehydrogenase (ADH; EC 1.1.1.1). Transgenic yeast expressing exogenous L-lactate dehydrogenase (L-LDH; EC 1.1.1.27) could produce lactic acid from pyruvic acid. Such metabolically engineered yeast were first reported by Dequin and Barre (8), Porro