Kinetics of Heat‐Shock Response and Inclusion Body Formation During Temperature‐Induced Production of Basic Fibroblast Growth Factor in High‐Cell‐Density Cultures of Recombinant Escherichiacoli

The kinetics of the heat‐shock response and the formation of inclusion bodies in recombinant Escherichia coli TG1 were studied in glucose‐limited high‐cell‐density cultures in response to temperature‐induced production of human basic fibroblast growth factor (hFGF‐2), a protein which partially aggregates into inclusion bodies. The maximum synthesis rates of heat‐shock proteins were similar to those in a control cultivation with a strain carrying an expression vector without inducible structural gene. However, the maximum of induction for many heat‐shock proteins including DnaK, ClpB, and HtpG was reached at least 30 min later when synthesis of hFGF‐2 was simultaneously induced by the temperature upshift. During this first production phase, hFGF‐2 was exclusively deposited in the insoluble cell fraction. Thereafter, accumulation of soluble hFGF‐2 was observed, too, indicating that the recombinant protein needs heat‐shock chaperones for proper folding at elevated temperatures. Strong recombinant protein production prolonged the synthesis of the majority of heat‐shock proteins (including GroELS, DnaK, ClpB, and HtpG) even in a wildtype dnaK+ background. In contrast, the synthesis rates of the small heat‐shock proteins IbpA and IbpB declined within 1 h to preinduction values in control and hFGF‐2 producing cultures. In the producing cultivation, IbpA and IbpB synthesis ceased to an undetectable level when soluble hFGF‐2 started to accumulate, whereas the synthesis rates of the other heat‐shock proteins including those belonging to the DnaK and GroEL families remained high throughout the entire production phase.