Process optimization for large-scale production of TGF-alpha-PE40 in recombinant Escherichia coli: effect of medium composition and induction timing on protein expression.
The effects of medium composition and induction timing on expression of a chimeric fusion protein TGF-alpha-PE40 (TP-40) in Escherichia coli strain RR1 were examined using a complex medium at several fermentor scales. Two distinctive phases in E. coli catabolism were identified during fermentation based on preferential utilization between protein hydrolysate and glycerol. Maximum specific and volumetric productivities were achieved by inducing the culture when the cells were switching substrate utilization from protein hydrolysate to glycerol. By increasing the yeast extract concentration in the production medium, initiation of the catabolic switch was delayed until high cell mass was achieved. The final titer of TP-40 at the 15-L fermentation scale was doubled from 400 mg L-1 to 850 mg L-1 by increasing the yeast extract concentration from 1% to 4% (w/v) and delaying the time of induction. This fermentation process was rapidly scaled up in 180-L and 800-L fermentors, achieving TP-40 titers of 740 and 950 mg L-1, respectively.