Cloning of the malic enzyme gene from Corynebacterium glutamicum and role of the enzyme in lactate metabolism

Malic enzyme is one of at least five enzymes, known to be present in Coryne bacterium glutamicum, capable of carboxylation and decarboxylation reaction s coupling glycolysis and the tricarboxylic acid cycle. To date, no informa tion is available concerning the physiological role of the malic enzyme in this bacterium. The malE gene from C. glutamicum has been cloned and sequen ced. The protein encoded by this gene has been purified to homogeneity, and the biochemical properties have been established. Biochemical characterist ics indicate a decarboxylation role linked to NADPH generation. Strains of C. glutamicum in which the malE gene had been disrupted or overexpressed sh owed no detectable phenotype during growth on either acetate or glucose, bu t showed a significant modification of growth behavior during lactate metab olism. The wild type showed a characteristic brief period of exponential gr owth on lactate followed by a linear growth period. This growth pattern was further accentuated in a malE-disrupted strain (Delta malE). However, the strain overexpressing malE maintained exponential growth until all lactate had been consumed. This strain accumulated significantly larger amounts of pyruvate in the medium than the other strains.