Comparison of three procedures for isolating DNA from bacteria.

Three methods employing chloroform-isoamyl alcohol (CI), phenol, or enzymes, were evaluated for isolating DNA from Escherichia coli, Bacillus subtilis, and Arthrobacter globiformis. For the amounts of reagents employed at optimum conditions in the CI and phenol procedures, 0.4-0.9 mg of DNA/g wet weight of cells was isolated. Using the enzymatic procedure, approximately twice as much DNA was isolated. DNA isolated by the CI procedure contained 0.03-0.09% protein and 0.08-0.12% RNA. DNA isolated by the phenol procedure contained 0.02-0.05% protein and 2.2-2.6% RNA. DNA isolated by an enzymatic procedure, which is described in detail, contained 32.2-45.7% protein and 0.3-0.6% RNA. DNA isolated by all three procedures are double-stranded and at least 10(6) in molecular weight, as suggested by data from thermal transition analyses and transformations. These data emphasize that the desired characteristics of DNA for experimental purposes must be considered in selecting an isolation procedure.