Role of acid metabolism in Streptomyces coelicolor morphological differentiation and antibiotic biosynthesis

Studies of citrate synthase (CitA) were tarried out to investigate its role in morphological development and biosynthesis of antibiotics in Streptomyc es coelicolor. Purification of CitA, the major vegetative enzyme activity, allowed characterization of its kinetic properties. The apparent K-m values of CitA for acetyl coenzyme A (acetyl-CoA) (32 muM) and oxaloacetate (17 m uM) were similar to those of citrate synthases from other gram-positive bac teria and eukaryotes, CitA was not strongly inhibited by various allosteric feedback inhibitors (NAD(+), NADH, ATP, ADP, isocitrate, or alpha -ketoglu tarate). The corresponding gene (citA) was cloned and sequenced, allowing c onstruction of a citA mutant (BZ2). BZ2 was a glutamate auxotroph, indicati ng that citA encoded the major citrate synthase allowing flow of acetyl-CoA into the tricarboxylic acid (TCA) cycle. interruption of aerobic TCA cycle -based metabolism resulted in acidification of the medium and defects in mo rphological differentiation and antibiotic biosynthesis. These developmenta l defects of the citA mutant were in part due to a glucose-dependent medium acidification that was also exhibited by some other bald mutants, Unlike o ther acidogenic bald strains, citA and bldJ mutants were able to produce ae rial mycelia and pigments when the medium was buffered sufficiently to main tain neutrality, Extracellular complementation studies suggested that citA defines a oem stage of the Streptomyces developmental cascade.