Purification of an Enterobacter aerogenes plasmid DNA using MnCl2 as compaction agent.

Development of an efficient process for purification of DNA plasmids continues to be a technological challenge [1-3]. While earlier applications of DNA plasmids were mostly in cloning, the last few years have seen its increasing applications in gene therapy [1] and preparation of DNA vaccines [4]. A crucial step in the production process is the downstream processing stage which encompasses separation of plasmid DNA from cellular components of the host strain (including chromosomal DNA and its fragments). In the case where the intended applications are in therapeutics, it is also necessary to separate the plasmid from materials such as toxic solvents, mutagenic reagents, and animal-derived enzymes (e.g., bovine pancreatic RNase A, used for removal of abundant RNA present in cell lysate) which may have been used in the production process. The existing protocols for plasmid production are, in general, time consuming, expensive, and difficult to scale-up [5]. Almost all of these require at least one chromatographic step although recently a process using a multicompartment electrolyser separated by ultrafiltration has been described [6].