Improved stability and expression of a recombinant shuttle plasmid in Escherichia coli during fedbatch cultivation

The effect of higher cell densities on the expression and segregational sta bility of a recombinant E. coli- B. subtilis shuttle plasmid coding for car boxymethylcellulase (CMCase) activity, was studied in E. coli DH5 alpha. Of the various feeding policies adopted for maximal expression and stability, exponential feeding resulted in the highest biomass of 15g dry cell weight (DCW) l(-1) and plasmid stability of 45%. A CMCase activity of 11400 U ml( -1) was achieved as compared to 230 U ml(-1) during batch cultivation. In t he case of other feeding strategies viz., constant feeding, linear feeding or intermittent feeding, the plasmid stability varied between 20% to 60%. B iomass achieved ranged from 5.0 g DCW l(-1) to 9.0 g DCW l(-1) and enzyme a ctivities were between 2550 U ml(-1) and 6000 U ml(-1).