Enhancement of Palmarumycins C12 and C13 Production in Liquid Culture of Endophytic Fungus Berkleasmium sp. Dzf12 after Treatments with Metal Ions

The influences of eight metal ions (i.e., Na⁺, Ca²⁺, Ag⁺, Co²⁺, Cu²⁺, Al³⁺, Zn²⁺, and Mn⁴⁺) on mycelia growth and palmarumycins C₁₂ and C₁₃ production in liquid culture of the endophytic fungus Berkleasmium sp. Dzf12 were investigated. Three metal ions, Ca²⁺, Cu²⁺ and Al³⁺ were exhibited as the most effective to enhance mycelia growth and palmarumycin production. When calcium ion (Ca²⁺) was applied to the medium at 10.0 mmol/L on day 3, copper ion (Cu²⁺) to the medium at 1.0 mmol/L on day 3, aluminum ion (Al³⁺) to the medium at 2.0 mmol/L on day 6, the maximal yields of palmarumycins C₁₂ plus C₁₃ were obtained as 137.57 mg/L, 146.28 mg/L and 156.77 mg/L, which were 3.94-fold, 4.19-fold and 4.49-fold in comparison with that (34.91 mg/L) of the control, respectively. Al³⁺ favored palmarumycin C₁₂ production when its concentration was higher than 4 mmol/L. Ca²⁺ had an improving effect on mycelia growth of Berkleasmium sp. Dzf12. The combination effects of Ca²⁺, Cu²⁺ and Al³⁺ on palmarumycin C₁₃ production were further studied by employing a statistical method based on the central composite design (CCD) and response surface methodology (RSM). By solving the quadratic regression equation between palmarumycin C₁₃ and three metal ions, the optimal concentrations of Ca²⁺, Cu²⁺ and Al³⁺ in medium for palmarumycin C₁₃ production were determined as 7.58, 1.36 and 2.05 mmol/L, respectively. Under the optimum conditions, the predicted maximum palmarumycin C₁₃ yield reached 208.49 mg/L. By optimizing the combination of Ca²⁺, Cu²⁺ and Al³⁺ in medium, palmarumycin C₁₃ yield was increased to 203.85 mg/L, which was 6.00-fold in comparison with that (33.98 mg/L) in the original basal medium. The results indicate that appropriate metal ions (i.e., Ca²⁺, Cu²⁺ and Al³⁺) could enhance palmarumycin production. Application of the metal ions should be an effective strategy for palmarumycin production in liquid culture of the endophytic fungus Berkleasmium sp. Dzf12.