Home About us MoEF Contact us Sitemap Tamil Website  
About Envis
Whats New
Research on Microbes
Microbiology Experts
Online Submission
Access Statistics

Site Visitors

blog tracking

Vol. 66, No: xx, 2007, Pages: 1670–1676

Bioremediation of cadmium contaminated soil using symbiosis between leguminous plant and recombinant rhizobia with the MTL4 and the PCS genes

Akiko Ike, Rutchadaporn Sriprang, Hisayo Ono, Yoshikatsu Murooka, Mitsuo Yamashita *

Department of Biotechnology, Graduate School of Engineering, Osaka University, 2-1 Yamada-oka, Suita, Osaka 565-0871, Japan.


Cadmium contamination in rice grains is one of the important issues in Asian countries. We have developed a novel bio-remediation system based on the symbiosis between leguminous plant and genetically engineered rhizobia. We designed two types of recombinant rhizobia, carrying two genes, synthetic tetrameric metallothionein (MTL4) and cDNA encoding phytochelatin synthase from Arabidopsis thaliana (AtPCS). The MTL4 and AtPCS genes were transferred to Mesorhizobium huakuii subsp. rengei B3, which can infect and form nodules on Chinese milk vetch, Astragalus sinicus. The two genes were fused to the nolB or nifH promoter, which generated nodule specific expression of these genes in strain B3. The two recombinant strains, B3(pMPnolBMTL4nifHPCS) and B3::nifHMTL4(pMPnifHPCS), showed 25 and 12-fold increase in Cd concentration, in the free-living cells, respectively. When these recombinant strains established the symbiotic relationship with A. sinicus, the symbionts increased Cd accumulation in nodules by two-fold in hydroponic culture. The expression of the both MTL4 and AtPCS genes showed additive effect on cadmium accumulation in nodules. We also applied these recombinant bacteria to rice paddy soil polluted with Cd (1 mg kg-1 dry weight soil). The accumulation of Cd increased not only in nodules but also in the roots of A. sinicus infected by the recombinant rhizobia. The accumulation of Cd in the plant roots infected by B3(pMPnolBMTL4nifHPCS) achieved three-fold than that by the wild-type B3. After two months of cultivation of the symbiont, a maximum of 9% of Cd in paddy soil was removed. Thus, the symbiosis will be useful in phytoremediation for heavy metals.

Keywords:Phytoremediation, Cadmium, Symbiosis, Leguminous plant, Rhizobia,Mesorhizobium huakuii subsp,Arabidopsis thaliana,Astragalus sinicus,bioremediation.

Corresponding author: Tel +81 6 6879 4170; fax +81 6 6879 7418

E-mail: yamashita@bio.eng.osaka-u.ac.jp


Copyright © 2005 ENVIS Centre ! All rights reserved
This site is optimized for 1024 x 768 screen resolution