Escherichia coli plasmid production in fermenter.

Escherichia coli harboring a recombinant plasmid was grown in a fermenter to study the effects of selected process parameters on the growth of the microbe and on plasmid amplification with chloramphenicol treatment. Eighteen fermentations were carried out according to a statistical experimental design in which the fermentation temperature, pH, and turbidity of culture at the onset of plasmid amplification were the selected independent process variables. Static regression models describing the process were derived from the experimental results. It turned out that recombinant plasmid copy numbers could be influenced by controlling fermentation temperature and pH. The maximal copy number during bacterial growth phase and the optimal plasmid production were found to require fermentation conditions different from those needed for optimal bacterial growth and cell division. The conditions also differed significantly from those routinely used in research laboratories for plasmid preparation. The chloramphenicol treatment increased the plasmid copy number compared with chromosome numbers up to fivefold. Some of the data suggest that under certain conditions the number of chromosome molecules in E. coli cells may rise during the plasmid amplification stage. Statistical experimental design, a nucleic acid sandwich hybridization technique for plasmid quantification, and regression models proved to be useful in this study.