Effects of divalent metal cations on lovastatin biosynthesis from Aspergillus terreus in chemically defined medium

Effects of six divalent metal cations: Fe2+, Ca2+, Zn2+, Mg2+, Cu(2+)and Mn2+ on fungal cell growth and lovastatin biosynthesis were investigated by submerged cultivation of Aspergillus terreus in a modified chemically defined medium. The influences of different initial concentrations of the above six metal cations were also examined at 1, 2, and 5 mM, respectively. Cu2+ apparently inhibited the cell growth, but had no influence on biosynthesis of lovastatin. All of Fe2+, Ca2+, Zn2+, Mg2+ and Mn2+ promoted the cell growth and lovastatin biosynthesis in different extents. The highest biomass of 13.8 +/- A 0.5 g l(-1) and specific lovastatin titres of 49.2 +/- A 1.4 mg gDCW(-1) were obtained at the level of 2 and 5 mM in the presence of Zn2+, respectively. The values were improved double and 14.4-fold. Excess Zn2+ inhibited the cell growth, but enhanced lovastatin biosynthesis with an increment of 17.6 mg l(-1) per mM. The interactions of all metal cations slightly inhibited the lovastatin production comparing with the existence of Zn2+, Fe2+ and Mg2+ solely, yet remarkably improved the cell growth. These results suggest that the divalent metal ions Zn2+ or Fe2+ influence the production by regulating the action of key enzymes such as LovD or LovF in lovastatin biosynthesis.