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Whole-cell optical biosensor for mercury — operational conditions in saline water

The present study demonstrates the influences of chlorides, fluorides and bromides of potassium and sodium on the growth and Hg2+-induced bioluminescence of bioreporter Escherichia coli ARL1. In a Luria-Bertani medium (LB), cell growth was inhibited by concentrations of sodium and potassium fluorides above 0.2 mol L−1. The addition of NaCl increased cell tolerance to the toxic effects of fluorides and bromides. Lag periods of 10 h and more were observed for cultivations in LB without NaCl and with halides (NaCl, KCl, NaBr, KBr, NaF and KF) at concentrations lower than 0.06 mol L−1. In a phosphate buffer (PB), the bioluminescence of E. coli ARL1, induced with HgCl2, was increased by the addition of NaCl, KCl, NaBr, KBr, NaF and KF (concentration of 0–0.25 mol L−1). In a saline phosphate buffer (PBS), the maxima of induced bioluminescence declined to 50 %, in the case of NaF (0.12 mol L−1), and to zero for KF. An addition of tryptone to the induction medium increased induced light emission ten-fold. Concentrated artificial sea water (ASW) (70–100 % ASW) inhibited bioluminescence induction. The new detection assay with E. coli ARL1 made possible the detection of 0.57 µL−1 of HgCl2 in double-diluted artificial sea water (25 % ASW).