Interactions between cadmium and radiation in the killing of Escherichia coli

CdCl2 (10 microM) added to the growth medium caused an extension to the lag phase in the growth of Escherichia coli. Radiation sensitivity in the extended lag phase was increased, particularly at low radiation doses. However, exposure to Cd2+ did not affect log-phase cultures which are normally more sensitive than lag-phase cultures. The increase in radiation resistance normally seen in stationary phase was delayed and reduced. When the cells had adapted to growth in the Cd2+-containing medium, further Cd2+ exposure was ineffective unless a Cd2+-free medium was provided for several hours. Prior growth in 25 microM Zn2+ partially protected against the effects of Cd2+ on growth and radiation sensitivity.