Use of a simple mathematical model to predict the behavior ofEscherichia coli overproducing ?-lactamase within continuous single- and two-stage reactor systems

Effect of the growth conditions on the synthesis of a recombinant beta-1,4-endoglucanase in continuous and fed-batch culture

Continuous culture and fed-batch fermentations were used to test the behavior of the system Bacillus subtilis DN1885(pCH7) that synthesizes a recombinant beta-1,4-endoglucanase. Continuous culture experiments were focused on the study of the instability aspects of the system as well as determination of the biomass growth rate range at which the recombinant enzyme synthesis was improved. Fed-batch fermentations were carried out to study the possibility of enhancing recombinant enzyme synthesis through the control of medium addition. It was found that, in continuous culture fermentations, the culture is less unstable at low dilution rates (dilution rate < 0.1 h(-)(1)). Also, low dilution rates give a higher specific recombinant enzyme concentration (10 times more than that obtained at high dilution rates). In fed-batch fermentation, the final recombinant enzyme concentration can be manipulated through the medium addition strategy. To increase the recombinant enzyme concentration, the carbon source has to be fed slowly, otherwise enzyme synthesis is impaired due to catabolite repression. Therefore, an increase in the biomass concentration does not necessarily imply an increase in the recombinant enzyme concentration. Higher recombinant enzyme concentrations were found in fed-batch fermentations compared to those obtained in continuous culture.

A model system for the continuous production of a heterologous protein using a novel secretion promoting factor which operates in Escherichia coli

The 'PAS factor' whose gene has been cloned from a species of Vibrio, is a novel protein secretion factor which is functional in Escherichia coli cells. To demonstrate that practical use of the PAS factor gene is possible, we have constructed a model secretion vector 'pAS23'. Using this system, beta-lactamase was produced and secreted into the medium of a continuous culture system, after optimization of culture conditions.

Fermentation monitoring and process control

During the past year, several papers describing the potential of new sensor devices for application in real bioprocesses have been published. Biosensors, optical sensors, and immunosensors are all gaining in importance. At present, the development of correct/adequate interfacing of biosensors to bioprocesses is the major limitation on progress. On the basis of new analytical data, a more precise modeling and control of fermentations can now be performed. Recent research efforts attest to the increasing importance of this area in biotechnology.