Bioremediation of heavy metals through symbiosis between leguminous plant and rhizobium with engineered metallothionein and phytochelatin synthase genes

We developed a novel bioremediation system, symbiotic engineering, based on the symbiosis between leguminous plant, Astragalus sinicus and the recombinant rhizobium, Mesorhizobium huakuii subsp. rengei B3, by over expressing a synthetic tetrameric metallothionein gene (MTL4) and cDNA encoding the phytochelatin synthase (AtPCS) and the iron regulated transporter (AtIRT1) from Arabidopsis thaliana. In rice paddy soil, addition of recombinant strain B3 carrying a plasmid with the MTL4, AtPCS and/or AtIRT1 genes significantly increased the accumulation of cadmium in roots and nodules of A. sinicus. Thus, this system uses the advantages of both plants and rhizobium. In particular, the system can easily transform engineered genes to the host plant through infection with a recombinant rhizobium.