Optimization of medium composition for propagation of recombinant Escherichia coli

Recombinant protein production in heterologous hosts often seems a simpler and more effective way than its production by natural producer. The secretion of recombinant protein in Escherichia coli has many advantages comparing to than in insect or mammalian cells. The important factor for high-level recombinant protein production is the sufficient amount of E. coli biomass. Therefore, the aim of this study was to optimize the composition of propagation medium resulting in the maximum biomass yield of recombinant E. coli as the part of fermentation strategy for neuraminidase (NA) production. Three independent variables including glucose, asparagine and phosphate concentrations, and four dependent variables, such as biomass yield, residual concentrations of glucose or asparagine and pH of the propagation medium after fermentation, were chosen to the optimization by Response Surface Methodology (RSM). The optimal conditions for the maximum biomass yield expressed as dry cell weight (DCW) (16.57±0.55 g DCW.L−1) were as follows: glucose concentration of 39.37 mM, asparagine concentration of 62.68 mM and phosphate concentration of 14.80 mM. For this model, the predicted values for the responses are close to the experimental values. The yield of desired pET15b-neu plasmid from E. coli cells cultivated in optimized propagation medium was almost 23 % higher than in commonly used Luria-Bertani (LB) medium suggesting that asparagine may be involved in the induction of plasmid amplification.