Mercury detoxification using genetic engineered Nicotiana tabacum

Phytoremediation is a low cost alternative solution to soil contamination compared with traditional removal and/or disposal techniques. One of the phytoremediation technologies is the phytovolatilization, whereby the contaminant is not primarily accumulated in above-ground tissues, but is instead transformed by the plant into the atmosphere. The detoxification of highly toxic organmercurial compounds and subsequent volatilization of elemental mercury is a unique example for the successful phytoremediation based on genetic engineering approach. For mercury removal techniques we constructed a dicistronic construct containing the bacterial mercury detoxification genes merA and merB under the control of the Arabidopsis Actin2 promoter and terminator. The resulted construct was introduced to Agrobacterium competent cells using heat shock transformation method. In the mean time, we germinated tobacco (Nicotiana tabacum var. Gold leaf) seeds on MS media and infected leaf discs of 6-8 weeks tobacco seedlings with Agrobacterium containing Ti plasmid harboring merA/merB dicistronic construct. The results showed that about 90% of tobacco seedlings were carrying the mer genes. Tobacco seeds were collected from wild type and transgenic lines and tested for mercury resistance. The results showed that transgenic plants are resistant to both Phenyl Mercuric Acetate (PMA) and HgCl₂. The root length and dry weight of wild and transgenic seedlings growing on both media amended with mercury compounds and media without mercury (control) were scored. The results showed that the root lengths and dry weight of the transgenic lines are significantly higher by 60 and 17-folds, respectively, compared to wild type. The results showed clear evidence that the transgenic plants are resistant to both organic and inorganic mercury compounds and can be used to clean up mercury contaminated sites.