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.
ArmanP.1957 M.Sc. Thesis, University of London; quoted by AbdullaI., SmithS. M. 1963 Influence of chelating agents on the concentration of some nutrients for plants growing in soil under acid and under alkaline conditions. J. Sci. Fd Agric 14:98
ClarkD. S., ItoK., TymchukP.1965; Effect of potassium ferrocyanide on the chemical composition of molasses used in the citric acid fermentation. Biotech, db Bioeng 7:269
PirtS. J., CallowD. S.1958; Exocellular product formation by micro-organisms in continuous culture. 1. Production of 2:3-butanediol by Aerobacter aerogenes in a single stage process. J. appl. Bact 21:188