| This thesis describes investigations carried out to assess the ability of two genetically modified strains of E. coli to take up measurable amount of Hg2+ from ambient levels (ng/L) of solutions in the laboratory under different conditions of pH, temperature, DOC concentration and presence and type of nutrients. The fraction of internalized Hg2+ transferred from the periplasm to the cytosol as a function of time of exposure to the cation was also quantified. Both strains (M3T and M4) can express the Hg2+ binding cytosolic protein, metallothionein fused to glutathione sulfur transferase (GST-MT). The fusion protein was also isolated and quantified along with its Hg2+ content after uptake. M3T also expresses Hg2+ specific (mer) membrane transport proteins that facilitate Hg2+ uptake. The evaluation of the Hg 2+ uptake potential of these strains was conducted against a control native strain, JM 109. The goal of this work is to utilize at least one of these strains in achieving the daunting task of measuring bioavailable Hg in lakes. The M3T strain took up the highest amount of Hg2+, most of which was not bound to GST-MT. M4 on the other hand, took up a lesser amount of Hg2+ than the control, but all of its cytosolic Hg 2+ was associated with GST-MT, partly because the strain expresses twice as much fusion protein than the M3T strain. The transport proteins (merP and merT) are more important for Hg2+ uptake by the bacteria at environmental concentrations of the cation, than the binding proteins.; Key words. Genetically modified E. coli, M3T and M4 strains, merP and merT transport proteins, Glutathione sulphur transferase, metallothionein, mercury accumulation. |
