Bioprocess Technology- Fundamentals and Applications Chapt 4_Metabolic basis(15)

secondary metabolite pathways. 2) Nitrogen metabolite repression i.e. easily metabolisednitrogen sources like ammonium ions likewise repress secondary metabolite producingenzymes. 3) Repression of pathways or individual enzymes by inorganic phosphate.Metabolic regulatory mechanisms like these necessitate the use of special cultivationconditions like fed batch techniques to obtain reasonable production. The synthesis ofsecondary metabolites is further regulated by feed-back inhibition by the end product or byregulation of the synthesis of precursors used for its formation. To overcome such obstacles itis necessary to improve strains by mutation.

Secondary metabolism is not separated from the primary metabolism but, on the contrary,intimately connected to it because precursor molecules and building blocks are derived bothfrom catabolic and anabolic pathways. This network is illustrated in Fig. 4.10, which at thesame time provides a rationale for classification of antibiotics according to their origin in the

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