Transgenic tobacco plant expressing environmental E. coli merA gene for enhanced volatilization of ionic mercury.

The practicability of transgenic tobacco engineered to express bacterial native mercuric reductase (MerA), responsible for the transport of Hg2+ ions into cell and their reduction to elemental mercury (Hg0), without any codon modification for phytoremediation of mercury pollution was evaluated. Transgenic tobacco plants reduce mercury ions to the metallic form; take up metallic mercury through their roots; and evolve less toxic elemental mercury. Transformed tobacco produced a large amount of merA protein in leaves and showed a relatively high resistant phenotype to HgCl2 than wild-type. Results suggests that the integrated merA gene, encoding mercuric reductase, a key enzyme of bacterial mer operon, is stably integrated into tobacco genome, and translated to active MerA which catalyzed the bioconversion of toxic Hg2+ to least toxic elemental Hg0, and suggest that MerA is capable of reducing the Hg2+, probably via NADPH as an electron donor. The transgenic tobacco expressing merA volatilized significantly more mercury than wild-type plants. This is first time we are reporting the expression of bacterial native merA gene via the nuclear genome of Nicotiana tabacum and enhanced mercury volatilization from tobacco transgenics. The study clearly indicates that transgenic tobacco plants are reasonable candidates for the remediation of mercury contaminated areas.