Construction and characterization of a photosynthetic bacterium genetically engineered for Hg2+ uptake

A recombinant photosynthetic bacterium, Rhodopseudomonas palustris, was constructed to simultaneously express mercury transport system and metallothionein for Hg2+ removal from heavy metal wastewater. The effects of essential process parameters, including pH, ionic strength and presence of co-ions on Hg2+ uptake were evaluated. The results showed that compared with wild type R. palustris, recombinant strain displayed stronger resistance to toxic Hg2+, and its Hg2+ binding capacity was enhanced threefolds. In the range of pH 4–10, recombinant R. palustris maintained effective accumulation of Hg2+. The presence of 10 mg L−1 Mg2+, Ca2+, Zn2+ or Ni2+ did not significantly influence Hg2+ bioaccumulation by recombinant R. palustris from solutions containing 0.2 mg L−1 Hg2+, while Na+ and Cd2+ posed serious adverse effect on Hg2+ uptake. Furthermore, EDTA treatment experiment confirmed that different from wild type R. palustris that mainly absorbed Hg2+ on the cell surface, recombinant R. palustris transported most of the bound Hg2+ into the cells.