Metal-induced mutagenesis in the lacI gene of Escherichia coli

Abstract

Mutagenesis in the lacI gene of Escherichia coli has been examined in cells grown in the presence of beryllium, manganese or chromium compounds, metals with suspected mutagenic or carcinogenic potential. 2–3-fold increases in mutation frequency were produced by BeCl 2, McCl 2 and K 2Cr 2O 7. Among the cells grown in the presence of Be 2+, the frequency of amber and ochre mutants was 3-fold higher than the spontaneous background, suggesting that at least part of the increased mutagenicity was due to base-substitution mutations. The specificity of base-substitution mutations induced by Be 2+ and Mn 2+ in the lacI gene was analyzed. Among the amber mutations induced in cells growth in the presence of Be 2+, an increase in G:C→A:T transitions was detected. In contrast, following growth in Mn 2+, no increase in amber and ochre mutation frequencies was observed, and the mutational spectrum resembled that obtained spontaneously indicating that mutations induced by Mn 2+ in the lacI gene involve changes that do not yield nonsense mutations. These results suggest that metals may exert a number of different mutagenic effects and that these effects vary for each metal.