Since detailed analysis on trace metal concentration in A. niger media showed that citric acid production could be increased by combining low levels of Mn2+ with high levels of Fe2+ [11], and because Fe2+ is a cofactor of hemoglobin to bind oxygen, we investigated this combination using medium 13. This medium contained a high concentration of Fe2+ and no Mn2+. However, neither the itaconic acid nor the citric acid level was improved in our 96-well screen. So, probably under limited oxygen supply in this micro-titer cultivation condition, the oxygen uptake in medium 13 had not been improved compared to medium 1.