Col V plasmids and the resistance of Escherichia coli to divalent copper ions

Free organisms of both plasmid-free and plasmid-carrying strains of Escherichia coli were killed by incubation in water containing low levels of cupric ions. Sensitivity was temperature-dependent with killing being more marked at 20° or 25°C than at 10° or 15°C. In contrast to the effects of other inhibitors from natural waters (which affect free Col V⁺organisms more than Col^-ones), free Col^-and Col V⁺organisms were equally sensitive to kill by Cu²⁺. Attachment to glass beads essentially abolished sensitivity to cupric ions with full survival after exposure to 15 μ g/ml. This applied to both p⁺and p^-strains but attachment would have more effect on the survival of p⁺organisms in natural waters because some plasmids markedly enhance attachment.