Efficient Disruption of Escherichia coli for Plasmid DNA Recovery in a Bead Mill

The release kinetics of pDNA in a bead mill was studied. Samples taken during the process were analyzed to determine total pDNA (pDNA(t)) and supercoiled pDNA (pDNA(sc)) concentration. In order to identify important variables of the process and to develop an empirical model for optimal pDNA(t) and pDNA(sc) release, a two level 2(3) factorial design was used with variables: mill frequency, cell concentration, and bead size. The results were analyzed by response surface methodology. The optimized conditions for pDNA(t) yield 13.26 mg/g dcw (93.41% recovery), with a mill frequency of 30 Hz, a bead size of 0.10-0.25 mm, and a cell concentration of 20 g wcw/L. However, the optimized conditions for pDNA(sc) yield 7.65 mg/g dcw (92.05% recovery), with a mill frequency of 15 Hz, a bead size of 0.10-0.25 mm, and a cell concentration of 10 g wcw/L. Cell disruption in a bead mill was proved efficient for the release of pDNA(t) and pDNA(sc) compared to the alkaline treatment. The results obtained suggest a compromise between pDNA(sc) purity and recuperation in the process development.