The effect of ammonium ions in the medium on production of thiostrepton byStreptomyces laurentiiwas investigated. In batch cultures, the excessive initial concentration of ammonium ions inhibited thiostrepton production. Moderate feeding of ammonia accelerated, however, not only microbial growth but also thiostrepton production. Fed-batch cultures with various feed rates of ammonia and a kinetic study clarified the effect of ammonium ion consumption rate on thiostrepton production. A modified kinetic model is proposed that takes product inhibition and the influence of maximum thiostrepton content into account.
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