THE INFLUENCE OF ZINC, IRON, COPPER, AND MANGANESE ON THE PRODUCTION OF CITRIC ACID BY ASPERGILLUS NIGER II

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Abstract
When A. niger 72-4 was grown from conidia in stationary surface culture for the purpose of producing citric acid from sucrose, traces of Zn, Fe, Mn, and Cu had to be added in order to obtain high yields of the acid. Omission of any one of the trace elements caused a marked reduction in acid formation. Omitting Zn caused a 96% decrease, Fe a 91% decrease, Mn a 44% decrease, and Cu a 76% decrease. When sucrose was purified by cation exchange treatment, the yield of acid with the purified sucrose, even when optimum concns. of Zn, Fe, Mn, and Cu were present, was 17% lower than with unpurified sucrose, thus indicating need for some additional factor.