START-UP SENSITIVITY TO THE INITIAL-STATE OF A BATCH BIOREACTOR FOR ARECOMBINANT ESCHERICHIA-COLI IN A COMPLEX MEDIUM

The sensitivities with respect to the initial state of five key variab les describing the performance of a batch bioreactor have been compute d from an experimentally validated kinetic model. The system has a rec ombinant Escherichia coli strain containing the plasmid pBR Eco gap, w hich codes for glyceraldehyde-3-phosphate dehydrogenase (GAPDH) in a c omplex medium. Since previous studies have shown the start-up sensitiv ities to be particularly important, the initial 10% of the duration of fermentation was chosen as the time span. The sensitivities of the ce ll mass, GAPDH and acetate increased with time while those of glucose and yeast extract remained practically constant. Acetate has a crucial role as it functions as both a product and a reactant. With no acetat e in the inoculum, the sensitivities of acetate increased an order of magnitude faster than other sensitivities. However, upon addition of a cetate through the inoculum, its sensitivities decreased the fastest a nd stabilised beyond a starting concentration of about 1 g/l whereas o ther sensitivities stabilised after 5 to 6 g/l of initial acetate. A t hree-dimensional envelope in the space of acetate concentration-time-r elative sensitivity shows a locus of concentrations for minimum time-d ependent acetate sensitivity; this may be maintained through fed-batch operation.