Continuous cultivation of recombinant Escherichia coli: Existence of an optimum dilution rate for maximum plasmid and gene product concentration

Growth yield factors, plasmid stability, cellular plasmid content, and cloned gene product activity for Escherichia coli HB101 containing plasmid pDM246 were measured at several dilution rates in continuous culture. Cell mass yield per mass of glucose consumed declined with increasing dilution rate. There was no evidence of plasmid segregational instability in any experiments, none of which employed selective medium. Plasmid content per cell varied with population-specific growth rate as observed in earlier batch experiments with the same strain. Plasmid content declined with increasing specific growth rate following indication of a maximum number of plasmids per cell at specific growth rates of ca. 0.3 h(-1). Cloned gene product (beta-lactamase) activity exhibited a sharp maximum with respect to dilution rate in continuous culture. Qualitatively different results were observed in previous experiments in batch cultivation in which specific growth rate changes were effected by altering medium composition.