Continuous-culture studies on the regulation of tylosin biosynthesis

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Abstract
The metabolic regulation of tylosin synthesis by Streptomyces fradiae NRRL 2702 was studied in batch and chemostat cultures using a soluble synthetic medium. In batch culture a medium which diminished the trophophase‐idiophase kinetic pattern was used to assess the activities of the enzymes involved in tylosin synthesis. The enzymes methylmalonyl‐coenzyme A carboxyltransferase (EC 2.1.3.1) and propionyl‐coenzyme A carboxylase (EC 6.4.1.3) showed early enzymatic derepression, both enzymes reaching their highest specific activities after 72–96 fermentation. The activity of macrocin 3′ ‐O‐methyltransferase, the enzyme catalyzing the conversion of macrocin (tylosin C) to tylosin (tylosin A). also peaked at 72 h. The specific activities of the three enzymes showed close correlation with the qtylosin value. In chemostat cultures the activities of the enzymes and the intracellular level of the adenylate pool and energy charge were studied as a function of dilution rate. Under steady‐state conditions, increases in the specific growth rate repressed the enzymes activities with a concomitant increase in the intracellular level of the adenylate pool, while the adenylate energy charge remained almost constant and in the range 0.5–0.52. The highest specific activities of the enzymes were observed when D = 0.008 h −1. The specific rate of tylosin synthesis was inversely proportional to the specific growth rate and the intracellular level of adenylate pool. The pool of adenylate could be a nutritional parameter which had a considerable influence on the biosynthesis of tylosin.