Characteristics of fed-batch cultures of recombinant Escherichia coli containing human-like collagen cDNA at different specific growth rates.

Fed-batch cultures of recombinant Escherichia coli BL21 for producing human-like collagen were performed at different specific growth rates (0.1 approximately 0.25 h(-1)) before induction and at a constant value of 0.05 h(-1) after induction by the method of pseudo-exponential feeding. Although the final biomass (around 69 g l(-1)) was almost the same in all fed-batch cultures, the highest product concentration (13.6 g l(-1)) was achieved at the specific growth rate of 0.15 h(-1) and the lowest (9.6 g l(-1)) at 0.25 h(-1). The mean productivity of human-like collagen was the highest at 0.15 h(-1) (0.57 g l(-1)h(-1)) and the lowest at 0.1 h(-1) (0.35 g l(-1 )h(-1)). In the phase before induction, the cell yield coefficient (Y(X/S)) decreased when the specific growth rate increased, while the formation of acetic acid increased upto 2.5 g l(-1) at 0.25 h(-1). The mean product yield coefficient (Y(P/S)) also decreased with specific growth rate increasing. The respiration quotient (RQ) increased slightly with specific growth rate increasing before induction, and the mean value of RQ was around 72%. The optimum growth rate for human-like collagen production was 0.15 approximately 0.2 h(-1).