SUMMARY: The development of in submerged culture, in a medium containing starch, glucose, ammonium sulphate, corn-steep liquor and calcium carbonate, takes place in several phases which differ in their morphological and biochemical characteristics. The starting phase is characterized by the logarithmic growth of thick Gram-positive filaments of the primary mycelium. Nucleic acids and respiratory enzymes are being synthesized during this phase and free amino acids and inorganic phosphorus in the medium are being almost completely used up. A considerable amount of pyruvic acid is being produced and accumulated in the medium. No production of oxytetracycline and pigments takes place. In the phase of logarithmic growth the respiration of the culture reaches a maximum value of 500–700 ml. O/l./hr.; at this stage growth of the primary mycelium ceases and its hyphae undergo fragmentation. Pyruvic acid, which had accumulated in the medium in the phase of logarithmic growth, is rapidly used up during the fragmentation period. From the fragments of the primary mycelium long Gram-negative filaments of secondary mycelium start growing. Growth in this phase is accompanied neither by any significant increase of the respiration nor by excretion of pyruvic acid; deoxyribonucleic acid (DNA) synthesis is considerably slower than in the phase of logarithmic growth and the total amount of ribonucleic acid (RNA) is decreasing; oxytetracycline and pigments are being produced both by the growing secondary mycelium and in the subsequent stationary phase.


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