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Abstract
Addition of any of the chelating agents ethylenediaminetetra-acetic acid, diamino-cyclohexane-N, N-tetra-acetic acid or diethylenetriamine-penta-acetic acid at about 1.0 mM to a sugar+NH4NO3 +salts medium stimulated citric acid production by Aspergillus niger. The greatest stimulation (about tenfold) was obtained with EDTA (1.0 mM). In contrast, potassium ferrocyanide at 84 μM stimulated citric acid production about 20-fold. Ferrocyanide was effective only when present at the beginning of the mycelial growth period, whereas the chelating agents were effective at any time during the growth period. Stimulation of citric acid production by ferrocyanide could be repressed by transferring the mycelium to fresh medium without ferrocyanide, or by removal of the ferrocyanide precipitate in the medium. Analyses of the iron, copper and zinc contents of the mould mycelium are given. Ferrocyanide did not affect the copper and zinc contents of the mycelium: EDTA did not affect the iron, copper and zinc contents of the mycelium.
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