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Nitrogen regulation of avermectins biosynthesis in Streptomyces avermitilis in a chemically defined medium

The biosynthesis of avermectins was significantly affected by the nitrogen source used. The maximum yield of AVMs1) was achieved in a chemically defined medium with ammonium sulfate as the sole nitrogen source. Higher concentrations of ammonia inhibited the production of AVMs without the inhibition of the growth. AVMs of the group B were prevailing in the complex until 15 mM ammonium sulfate. At higher concentrations, AVMs of the group A predominated. Of various amino acids tested, lysine and asparagine were found to be the best for the biosynthesis of AVMs. The concentration of most amino acids higher than 0.2% inhibited the production, while the mycelium was still growing. The biosynthesis of AVMs was completely suppressed by 15.2 mM isoleucine, however, this inhibition was reversed by adding alanine at the beginning of cultivation.