The Effects of NH 4 + on L-tryptophan Fermentation

Objective:To study the effects of NH4+ on biosynthesis of L-tryptophan.Methods:Fed-batch fermentation of E.coli TRTH with addition of ammonium sulfate carried out in 30-Liter fermentor and biomass,yield of L-tryptophan,consumption rate of glucose,plasmid stability were measured.The concentration of acetate,NH4+,lactate and pyruvate were investigated by BioProfile 300A Nova and high performance liquid chromatography(HPLC).The metabolic flux balance model of L-tryptophan synthesis by E.coli was established.Based on this model,the practical metabolic flux distribution of E.coli TRTH were determined with the linear program planted in MATLAB software.Results:During the fed-batch culture,E.coli TRTH was able to maintain higher growth rate at exponential phase,finally,the biomass and the yield of L-tryptophan were increased by 51.07% and 46.54% respectively by controlling the concentration of NH4+ less than 120 mmol/L.As the increase of the concentration of NH4+,the concentration of pyruvate,lactate and acetate were slightly increased,but cell plasmid stability was decreased.Data indicated that EMP pathway and TCA cycle were decreased by 7.31% and 22.04% respectively,PP pathway was increased by 7.14% compared with addition 5g/L of ammonium sulfate at 14h during the fed-batch culture.Conclusion:High concentrations of NH4+ terminated the cell growth,decreased the consumption rate of glucose and inhibited the L-tryptophan production.Controlled the concentration of NH4+ less than 120 mmol/L,the biomass and the yield of L-tryptophan were significantly increased,which accessed high cell density cultivation.