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 Escherichia coli

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, CIpB, 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 heatshock proteins (including GroELS, DnaK, CIpB, and HtpG) even in a wildtype dnaK+ background. In contrast, the synthesis rates of the small heat-shock proteins IbpA and IbpB declined within I h to preinduction values in control and hFGF-2 producing cultures. In the producing cultivation, lbpA and lbpB 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.