Amplification of pBR322 plasmid DNA in Escherichia coli relA strains during batch and fed-batch fermentation

Fermenter studies under batch and fed-batch conditions were carried out to test the possibility of plasmid pBR322 production in large amounts by using E. coli relA strains. High amplification rates of pBR322 plasmid DNA were observed in E. coli CP79 (relA) and E. coli CP143 (relA) in both batch and fed-batch cultivation after exhaustion of the amino acid arginine. The concentrations of plasmid DNA per unit of biomass were nearly the same in batch and in fed-batch fermentations of E. coli CP79 and E. coli CP143. Therefore, the significantly higher biomass concentration of the two strains after fed-batch fermentation gave a dramatic increase in the yield of plasmid DNA per litre of medium in comparison to the batch process. The results support the suggestion that E. coli relA strains are suitable hosts for production of large amounts of ColE1-derived plasmids for recombinant DNA research.