Abstract
Nitrogen regulation of tylosin synthesis in Streptomyces fradiae NRRL 2702 was studied in batch and chemostat cultures using a soluble synthetic medium. In batch cultures, valine dehydrogenase (VDH; EC 1.4.1.8), threonine dehydratase (TDT; EC 4.2.1.16) and aspartate aminotransferase (ASAT; EC 2.6.1.1) reached their highest specific activities at 120 h. The specific activities of the three enzymes showed close correlation with the value of specific tylosin formation rate ( q TYL). In chemostat cultures, the maximum value of q TYL was 1.14 tylosin per mycelial mass per h (mg g −1 h −1) at the specific growth rate of 0.05 h −1, and after reaching a rate of 0.1 h −1, q TYL decreased with increasing levels of the specific growth rate. This value of q TYL was 3.5-times as large as that of maximum q TYL observed in the batch culture. The specific formation rates of VDH, TDT, ASAT and tylosin were repressed by high levels of specific ammonium ion uptake rate.
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