Toxicity of free and various aminocarboxylic ligands sequestered copper(II) ions to Escherichia coli.

Cytotoxicity of free Cu(II) ions and its complexes of EDTA, NTA or IDA in Escherichia coli (AB 4401) wild type cells were assessed by cell inactivation assay. In order to understand the toxic effects of these additives, membrane status by AFM vis-à-vis K(+) ion efflux were followed in the absence and in the presence of Cu(II) ions or its complexes. This was coupled with the determinations of cellular copper concentrations by atomic absorption spectrometry. The observed results show that free copper ions are more cytotoxic and cause considerable plasma membrane damage compared to that of Cu-EDTA, Cu-NTA and Cu-IDA. Determination of cellular copper reveals that Cu(2+) and Cu-NTA are able to enter inside the cells while Cu-EDTA and Cu-IDA fail to do that. This may be attributed to the electron affinity of free Cu(2+) ions and Cu-NTA, which help in binding with histidine present in copper transport proteins. In addition to cytotoxicity, genotoxicity of free copper and its complexes were also assessed on E. coli isogenic DNA repair proficient and repair-deficient strains. In contrast to free Cu(2+) ions, Cu-NTA does not cause any significant cytotoxicity but render greater genotoxicity.