Succinate-mediated catabolite repression of enzymes of glucose metabolism in root-nodule bacteria

Enzymes of the Embden-Meyerhof-Parnas and Entner-Doudoroff pathways were detected in strains ofRhizobium andBradyrhizobium cultured on glucose. The enzymes, except glyceraldehyde-3-phosphate dehydrogenase, were present only in trace amounts in succinategrown cells. The enzymes of the pentose phosphate pathway, being absent inBradyrhizobium, were detected only in glucose-grown cells ofRhizobium. The presence of the glucose-catabolic enzymes in cells only during growth on glucose suggests that they are inducible in nature. Succinate repressed the glucose catabolic enzymes, and the repression appeared to be similar to catabolite repression. Exogenous addition of cAMP caused no change in the activity of these enzymes, demonstrating that the repression was unlikely to be mediated via cAMP.