Rheological properties of chromosomal and plasmid DNA during alkaline lysis reaction

The recovery of plasmid DNA from cells is achieved by a two-step chemical reaction which usually employs sodium hydroxide and sodium dodecyl sulphate followed by neutralisation with a chilled solution of potassium acetate. It is important that the gelatinous flee of chromosomal DNA with proteins debris is not broken down since fragments of chromosomal DNA are difficult to separate from plasmid DNA. To accomplish the operation at scale demands knowledge of the rheology as the reactions proceed. In this paper a co-axial cylinder rheometer is used to record the changes for two strains of Escherichia coli cells. Analysis of the liquor, prior to neutralisation indicates that at shear rates below 367 s(-1) the flow properties during lysis are non-Newtonian, but above 367 s(-1) flow behaviour becomes Newtonian. Additionally, following neutralisation, the rheological data show that the clear liquor obtained at low shear levels is Newtonian, but the gelatinous floc has strong viscoelasticity. These properties strongly influence subsequent stages for the removal of solids.