REGULATION OF ACETATE METABOLISM IN CORYNEBACTERIUM-GLUTAMICUM - TRANSCRIPTIONAL CONTROL OF THE ISOCITRATE LYASE AND MALATE SYNTHASE GENES

In the amino-acid-producing microorganism Corynebacterium glutamicum, the specific activities of the acetate-activating enzymes acetate kina se and phosphotransacetylase and those of the glyoxylate cycle enzymes isocitrate lyase and malate synthase were found to be high when the c ells were grown on acetate (0.8, 2.9, 2.1, and 1.8 U/mg protein, respe ctively). When the cells were grown on glucose or on other carbon sour ces such as lactate, succinate, or glutamate, the specific activities were two-to fourfold (acetate kinase and phosphotransacetylase) and 45 - to 100-fold (isocitrate lyase and malate synthase) lower, indicating that the synthesis of the four enzymes is regulated by acetate in the growth medium. A comparative Northern (RNA) analysis of the C. glutam icum isocitrate lyase and malate synthase genes (aceA and aceB) and tr anscriptional cat fusion experiments revealed that aceA and aceB are t ranscribed as 1.6-and 2.7-kb monocistronic messages, respectively, and that the regulation of isocitrate lyase and malate synthase synthesis is exerted at the level of transcription from the respective promoter s. Surprisingly, C. glutamicum mutants defective in either acetate kin ase or phosphotransacetylase showed low specific activities of the oth er three enzymes (phosphotransacetylase, isocitrate lyase, and malate synthase or acetate kinase, isocitrate lyase, and malate synthase, res pectively) irrespective of the presence or absence of acetate in the m edium. This result and a correlation of a high intracellular acetyl co enzyme A concentration with high specific activities of isocitrate lya se, malate synthase, acetate kinase, and phosphotransacetylase suggest that acetyl coenzyme A or a derivative thereof may be a physiological trigger for the genetic regulation of enzymes involved in acetate met abolism of C. glutamicum.