Patent ID: 7378238

Claim:
A method of making a clear cell lysate containing plasmid DNA from a biomass obtained in a cell culture process, said method consisting of the steps of: a) suspending the biomass together with a filtering agent to form a first suspension, wherein the filtering agent is a kieselguhr and said kieselguhr contains greater than or equal to 90% silica, a wet density of 0.2 to 0.4 g/cm 3 , a permeability of 0.02 Darcy, a BET surface area of 2 to 20 m 2 /g, a geometrical surface area of 0.25 to 0.65 m 2 /g , a particle size of 2.5 to 8.0 μm, and a 99% particle size retention of 0.1 to 0.2 μm; b) filtering the first suspension in the presence of the filtering agent with a filter medium to form a filter cake containing said biomass; c) after the filtering of step b), re-suspending the filter cake formed during said suspending in a lysis buffer at pH 7 to 10 to form a second suspension, wherein the lysis buffer consists of 150 mmol of Tris-HCL, 25 mmol of Na 2 EDTA, 8% by weight of sucrose, and optionally containing 2% TritonX-100®; d) heating said second suspension at temperatures between 70° C. to 90° C. for at least 30 seconds to thermally digest said biomass; e) after the heating of step d), filtering said second suspension with the filter medium in the presence of the filtering agent to obtain the cell lysate; wherein said filtering of said second suspension and said first suspension consists of filtering only with the aid of vacuum or pressure; f) filtering the cell lysate to form a clear filtrate containing said plasmid DNA and having a clarity OD 600 of not more than 0.05 U/cm, which corresponds to a decrease of turbidity of at least 99%, and in which said method does not include centrifugation.