Metabolic Analysis of <i>Corynebacterium glutamicum</i> during Lactate and Succinate Productions under Oxygen Deprivation Conditions

Lactate and succinate were produced from glucose by <i>Corynebacterium glutamicum</i> under oxygen deprivation conditions without growth. Addition of bicarbonate to the reaction mixture led not only to a 3.6-fold increase in succinate production rate, but also to a 2.3- and 2.5-fold increase, respectively, of the rates of lactate production and glucose consumption, compared to the control. Furthermore, when small amounts of pyruvate were added to the reaction mixture, acid production rates and the glucose consumption rate were multiplied by a factor ranging from 2 to 3. These phenomena were paralleled by an increase in the NAD⁺/NADH ratio, thus corroborating the view that the efficient regeneration of NAD⁺ could be triggered by the addition of either bicarbonate or pyruvate. To investigate the global metabolism of corynebacteria under oxygen deprivation conditions, we engineered several strains where the genes coding for key metabolic enzymes had been inactivated by gene disruption and replacement. A lactate dehydrogenase (LDH)-deficient mutant was not able to produce lactate, suggesting this enzyme has no other isozyme. Although a pyruvate carboxylase <i>(pyc)</i> mutant exhibited similar behavior to that of the wild type, phosphoenolpyruvate carboxylase <i>(ppc)</i> mutants were characterized by a dramatic decrease in succinate production, which was concomitant to decreased lactate production and glucose consumption rates. This set of observations corroborates the view that in coryneform bacteria under oxygen deprivation conditions the major anaplerotic reaction is driven by the <i>ppc</i> gene product rather than by the <i>pyc</i> gene product. Moreover, intracellular NADH concentrations in <i>C. glutamicum</i> were observed to correlate to oxygen-deprived metabolic flows.