Figure 4.

Effect of adding time of validamine on the acarbose production (a), impurity C formation (b), and cells growth (c) in batch culture by A. utahensis ZJB-08196. Fermentation was carried out at 28°C and 200 rpm for 168 h in fermentation medium with the addition of validamine at a final concentration of 20 mg/L and 40 mg/L at a different cultivation time. The error bars in the figure indicate the standard deviations from three independent samples. *indicates statistic significance (P < 0.05) compared to control experiments without the addition of validamine.