The tolerance of an environmental strain of Escherichia coli to some heavy metals.

The effect of mercury, cadmium, copper, zinc, chromium and lead on an environmental strain of Escherichia coli was studied. The tolerance growth limits, growth kinetics and viability were determined. It was found that metal-ion concentrations greater than the threshold values (0.005 microM Hg2+, 0.5 microM Cd2+, 5 microM Cu2+, 23 microM Cr3+, 30 microM Zn2+, 45 microM Pb2+) increase the lag-phases but do not modify the growth kinetics (Pb2+ is an exception). During the lag-phase a reduction in cell viability, varying from a maximum of 89% for lead, to a minimum of 13% for cadmium, was observed. The reduction of viability accounts for a cells physiological adaptation to the metals rather than selection of resistant mutants. Loss of the acquired metal resistance following exposure of the bacterial cells to the metals supported this last point.