The levels of itaconic acid, citric acid and oxalic acid of A. niger transformant AB 1.13 CAD pyr + 4.1 in medium 12 containing three concentrations of copper were analyzed. As presented in Figure 3A, the production rate of itaconic acid is positively correlated with the copper concentration while this correlation is different for citric acid (Figure 3B) and oxalic acid (Figure 3C). In the low-copper medium (0.005 mM Cu2+), high levels of oxalic acid are accumulated whereas the highest amount of citric acid is produced in the medium-copper medium. In addition to organic acids, we determined biomass and glucose consumption. Glucose consumption of A. niger strain AB 1.13 CAD pyr + 4.1 among all three media is nearly the same (Figure 4). Increase in biomass showed a strong positive correlation with copper levels (Figure 4). The three main organic acids were quantified and the average concentrations (g/L) of duplicate measurements are listed in Table 4. As indicated, a two fold increase of the percentage of itaconic acid is obtained in the high-copper medium. (Table 4).