Metallic ions as a component required of culture media, havebeen proved to play an important role in the cell growth, γ -PGA
yield, stereochemical composition and molecular weight of γ -PGAproducing strain. For example, γ -PGA yield was increased in thepresence of Ca2+ in the B. subtilis CGMCC 2108 [4]. Mn2+ has an effect on prolonging the viability of cells which lead to the γ -PGA yield increased, and increasing the proportions of D-isomers of γ -PGA in Bacillus licheniformis 9945A