Effect of Adding Metal Ions on γ-Poly(glutamic acid) Production by Bacillus cereus

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.