Influence of the medium composition and plasmid combination on the growth of recombinant Escherichia coli JM109 and on the production of the fusion protein EcoRI::SPA

Plasmid-free and plasmid-harbouring E. coli JM109 strains were investigated in shaken flasks, stirred tanks in batch and continuous operation. The shaken flask cultivations were performed in M9 minimal medium and in media with various protein supplements. The host hardly grows on M9 minimal medium as opposed to the plasmid-harbouring cells, which grow well on this medium. All of the investigated cells propagate well on protein-containing media. The influence of the combinations of repressor plasmid pRK248cI, the protection plasmid EcoR4 and the production plasmid pMTC48 were determined on the initial specific growth rate of the E. coli JM109 without gene expression, on the yield coefficient of cell growth, acetate concentration and acetate yield coefficient in the yeast extract-containing (HM) medium. The influence of various media on the induction of the gene expression were evaluated. In cultivation media with protein supplement, the growth rate and yield coefficient increased. The variation of the volumetric and specific beta-lactamase activities with the cultivation time were determined in a stirred tank reactor in HM medium. With increasing dilution rate the process performance decreased. Simple relationships exist between the substrate uptake rate and the specific growth rate of the continuous cultivated cells in M9 and HM media. The influence of the dilution rate on the cell mass concentration, colony forming units, acetate formation, yield coefficients of growth and acetate formation, substrate uptake rate, CO2 production rate, ammonium formation rate and beta-lactamase activity in M9 and HM media were determined as well. Carbon balances of the batch and continuous cultivations indicated high carbon recoveries. On account of the higher growth rate of plasmid-harbouring cells than than of the plasmid-free cells, the behaviour of the investigated plasmid-free and plasmid-harbouring E. coli JM109 cells deviates from the published properties of other plasmid-free and plasmid-harbouring E. coli cells.

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.