In the following experiments, the optimal addition conditions as identified above were adopted to demonstrate the dynamic profiles under the positive effect of ferrous sulfate addition on cell growth and cordycepin production. As the results shown in Fig. 3, no obvi-ous difference in change patterns of biomass, medium pH and glucose utilization was noticed between the cases with and with-out iron addition, which was similar to other reports on Cordyceps [13,14,34]. The cell density reached the maximum on day 10 in the iron-treated cultures and on day 15 in the control, i.e., 15.86 ± 0.28 and 15.71 ± 0.35 g/L, respectively. Meanwhile, the growth rate in both conditions from day 4 to day 10 was the fastest throughout the entire cultivation. Interestingly, iron addition seemed to stim-ulate cell growth after 4 days compared to the control, resulting in a higher and earlier peak of the biomass. The patterns of pH change and glucose consumption in these two conditions were also similar. The medium pH quickly decreased from 6.0 to about 3.0 until day 4 in both cases, possibly because of the continuous con-sumption of carbon and nitrogen sources which would produce lots of acidic metabolites. After 15 days cultivation, the pH showed a slight increase and then remained constant to the same level (about pH 2.2), implying that the release of acidic metabolites may be similar for the two cases. A similar phenomenon of pH change was also reported [15]. Another report claimed that daily con-trol of pH could highly improve cordycepin content compared to