A completely automated system for on-line monitoring of the production of a growth factor secreted during fermentation of Escherichia coli.

The production of IGF-1 (insulin-like growth factor 1), expressed in Escherichia coli as a secreted fusion protein with affinity for the Fc region of IgG, was monitored automatically during fermentations. A sampling device was used to automatically inject filtered culture medium from the fermentor onto a small affinity column (IgG Sepharose(R) Fast Flow) connected to a chromatographic system. The area of the eluted peak was proportional to the concentration of the fusion protein. The relationship was linear over the range 25-630 microg/mL with relative standard deviation of around 1% at the higher concentrations. Samples could be monitored automatically every half hour during fermentation (48 h). The method of analysis is nondestructive, allowing further analysis of product quality. A complete evaluation of the monitoring system is described. With this system, fermentations based on the described expression system can be optimized on the basis of product concentration; this will lead to more effective fermentations and higher product yields. It should also be possible to monitor other secreted products with this system by using other affinity gels.