Regulatory Effect of Pyruvate on the Glucose Metabolism of Clostridium thermosaccharolyticum

Whole cells and cell-free extracts of Clostridium thermosaccharolyticum 3814 grown in media containing 0.5% glucose or 0.6% pyruvate were evaluated for their metabolic activities toward these compounds. Glucose-grown cells rapidly fermented glucose with the production of gases (CO₂ and H₂), acids, and alcohol, but they did not ferment pyruvate well. Pyruvate-grown cells, on the other hand, readily fermented pyruvate, while fermenting glucose at a rate of one-half that of pyruvate. An analysis of the enzyme levels in the two cell culture conditions revealed that pyruvate-grown cells had lower levels of most of the glycolytic enzymes and increased levels of the hexose monophosphate pathway enzymes. Incorporation studies with the use of labeled glucose demonstrated that cells do have a control mechanism(s) whereby they can discriminate between a carbon (glucose) and an energy (pyruvate) source, selectively utilizing glucose in the synthetic pathway while obtaining energy from the phosphoroclastic degradation of pyruvate.