The Origin of Bacterial Resistance to Proflavine: 5. Transformation of Proflavine Resistance in Escherichia coli

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Abstract
We attempted to transform proflavine-sensitive strains of Escherichia coli to proflavine resistance by growth in the presence of deoxyribonucleic acid-containing extracts from resistant organisms. Three methods were used to obtain the DNA preparations. Method 1 did not give active transforming principle, even when a variety of modifications was introduced. Method 2 and Method 3 gave extracts that were active in transformation. With DNA prepared by Method 2, an increase in the number of resistant organisms was found in one out of 4 rough sensitive strains. Apparently only a small proportion of the organisms of this strain were competent. We were able to increase the proportion of these competent organisms by a "double replica plating" According to Method 3, organisms were lysed by sodium dodecylsul-phate (Duponol) in presence of citrate, and protein removed by sodium acetate. From the supernatant fluid transforming principle was precipitated by acidified ethanol, then dissolved in saline. The smooth strain of Escherichia coli used in most of our experiments served as the recipient strain. The transforming principle from resistant organisms was not active alone., but was active in the presence of the protein precipitate. The activity appeared to be lost when the extract was treated with DNAase. No activity was shown by extracts from sensitive organisms. The activation of transforming principle by the protein precipitate is thought to be due to the Duponol carried with it. Duponol inhibits DNAase and it might act by preserving transforming DNA in the recipient organisms. The experiments did not always give positive results.