Enhanced DNA uptake and transfection in Escherichia coli cells grown in low-phosphate medium

Abstract

1. The very limited ability of Escherichia coli wild type cells to take up DNA has been found to persist in endonuclease I-deficient cells, from which DNA can be recovered undegraded after co-incubation. 2. Addition of protamine sulphate promotes essentially reversible adsorption when incubation of DNA with the cells is carried out at 32° or 37°. However, a significant enhancement of irreversible incorporation takes place at 4°, both in protamine-treated cells and for partially starved cultures kept at the low temperature. 3. The greatest incorporation of DNA correlating with transfecting ability is found in osmotically treated EDTA-“permeable” cells grown in either Tris-buffered or phosphate-deficient media which incorporate much more DNA than similarly treated cells grown in phosphate-buffered medium. 4. On the basis of the greater DNA incorporation found both in normal and in osmotically shocked “permeable” cells grown in low-phosphate medium which correlates with a greater transfection efficiency for ΦX174 DNA, it is postulated that a competent state of E. coli may be related to a state of phosphate limitation.