Crabtree neg. organisms such as Kluyveromyces, Pichia, Hansenula and Candida, are used to make selected org. products such as lactic acid. The organisms are cultured in a first culture medium that includes glucose, under conditions that promote cellular respiration. The organisms are then cultured under a second set of conditions that promote prodn. of the selected org. product. The organisms preferably contain an exogenous lactate dehydrogenase gene. Thus, gene PDC1 encoding pyruvate decarboxylase in Kluyveromyces marxianus was disrupted by site-directed mutagenesis. The LDH gene from Kluyveromyces thermotolerans under control of the Saccharomyces cerevisiae PDC1 promoter was then introduced to this Kluyveromyces marxianus strain by electroporation. The resulting strain was able to produce lactic acid using aerobic conditions for cell growth and anaerobic conditions for lactate prodn. [on SciFinder (R)]