Influence of controlled glucose oscillations on a fed-batch process of recombinant Escherichia coli

The influence of glucose oscillations on cell growth and product formation of a recombinant Escherichia coli culture producing a heterologous alpha-gl ucosidase was studied in fed-batch cultures in a laboratory bioreactor. Glu cose oscillations were created by an on/off-feeding mode in either fast cyc les (1 min) or slow cycles (4 min) and compared to a process with constant glucose addition. The study indicates that glucose oscillations influence t he product stability and the overgrowth of plasmid-free cells if such cultu res are not performed under continuous pressure for selection of plasmid-co ntaining cells. Although the glucose uptake capacity decreased after induct ion of the recombinant alpha-glucosidase in all cultures performed, the up- growth of plasmid-free cells during the production phase was strongly inhib ited by fast oscillations. In contrast, plasmid-free cells grew up when con stant feeding or slow cycles were applied. Our data suggest that the variou s feed protocols effect the specific carbon dioxide formation rate differen tly, with the highest production of carbon dioxide in the cultivations with fast cycles. In connection to product formation the initial alpha-glucosid ase accumulation was the same in all cultures, but the stability of the pro duct was significantly lower in the cultivation with slow cycles. Our resul ts from laboratory experiments are discussed in relation to the mixing situ ation in large-scale bioreactors. (C) 2000 Elsevier Science B.V. All rights reserved.