Abstract: In this paper, the effects of some metal ions on the synthesis of poly-γ-glutamic acid (γ-PGA) by Bacillus cereus was investigated. Varied amounts of Mn2+, K+, Fe3+, Mg2+, Ca2+, Mo6+, Zn2+, Co2+, Cd2+ and Cu2+  were respectively added into the culture medium and their consumption, bacterial biomass, and the yield of γ-PGA were measured during fermentation at regular time intervals by atomic absorption spectrophotometry. The effects of Mn2+ alone, Mn2+ (at 0.08 g/L) plus Ca2+ at different concentrations, Mn2+ (at 0.08 g/L concentration) plus Ca2+ (at 1.0 g/L concentration) plus Zn2+, Co2+ or Mo6+ at different concentrations on bacterial biomass and the yield of γ-PGA at the end of fermentation were investigated. The results showed that during the synthesis of γ-PGA, certain amounts of Mn2+, K+, Fe3+, Mg2+, Ca2+, Mo6+, Zn2+ and Co2+ were consumed, among which Mn2+, K+, Fe3+, Mg2+ and Ca2+ displayed a higher amount, while the concentrations of Cd2+ and Cu2+ were kept unchanged. Mn2+ was found to be neccessary for the synthesis of γ-PGA, and when its concentration was 0.08 g/L, γ-PGA synthesis reached its peak (1.25 g/L). When the concentration of Mn2+ was fixed at 0.08 g/L, increasing Ca2+ concentration could greatly increase γ-PGA synthesis; when the concentrations of Mn2+ and Ca2+ were fixed, the addition of Zn2+ promoted γ- PGA synthesis significantly, up to 2.94 g/L, and adding Mo6+ had no obvious effect on the synthesis of γ-PGA, but a greater impact on bacterial biomass.

Key words: Bacillus cereus, poly γ-glutamic acid, metal ions