EFFECT OF FERROCYANIDE ON GROWTH AND ACID PRODUCTION OF ASPERGILLUS NIGER

Growth of Aspergillus niger, in a simple synthetic medium, is inhibited by ferrocyanide ion in concentrations below 1 p.p.m. This inhibition can be reversed by increasing the iron and zinc concentration of the medium. Acid production, however, is inhibited only 50% by 200 p.p.m. ferrocyanide and this inhibition is not reversible by trace metals. Neither the inhibition of growth nor that of acid production is the result of release of cyanide from ferrocyanide. It is suggested that ferrocyanide has at least two functions in the treatment of substrates for use in the production of citric acid. The first is to remove deleterious trace metals from the medium whereas the second is to act as a direct inhibitor of growth of the mold.