Single strand breakage in DNA of Escherichia coli exposed to Cd2

Abstract

When a growing culture of E. coli was exposed to 3 x 10-6 M Cd2+, 85 to 95% of the cells lost their ability to form colonies on agar plates. Loss of viability was accompanied by considerable single-strand breakage in the DNA, with no detectable increase in double-strand breaks. A direct correlation appeared to exist between the number of single-strand breaks and the concentrations of Cd2+ to which the cells were exposed. Exposure of DNA in vitro to a Cd2+ concentration of 3 x 10-6 M or higher, followed by sedimentation in alkaline sucrose gradients, demonstrated no single-strand breaks. Cadmium-exposed cells recovered viability when incubated in Cd2+ free liquid medium containing 10 mM hydroxyurea. During the early period of recovery, there was a lag in the incorporation of labeled thymidine, but cellular DNA, at least in part, appeared to be repaired.