Assessment of iron toxicity using a luminescent bacterial test with an Escherichia coli recombinant strain

The toxic effect of the Fe2+ and Fe3+ ions on the luminescent recombinant Escherichia coli strain with the luxCDABE operon was studied in short- and long-term experiments. At 30-min exposure of bacteria to the iron ions, the effective concentrations of Fe2+ and Fe3+ resulting in acute toxicity (EC50) were 8.5 and 1.3 mg/L, respectively. In the long-term (24 h) experiment, during active bacterial growth, the toxicity index for Fe2+ and Fe3+ was 65.5 and 62.8, respectively. Addition of the iron ions into the medium did not suppress growth, although it inhibited luminescence. Comparative analysis of the short- and long-term experiments made it possible to assess iron toxicity at the concentrations from 0.5 to 20 mg/L (as calculated for the Fe2+ and Fe3+ ions). Iron ions were found to affect only the reactions that were not vitally important for the cell. At the same time, they had no negative effect on the genetic mechanisms and protein synthesis, thus indicating non-specific toxicity of Fe2+ and Fe3+.