Ike Akiko, Sriprang Rutchadaporn, Ono Hisayo, Murooka Yoshikatsu, Yamashita Mitsuo
Department of Biotechnology, Graduate School of Engineering, Osaka University, Suita, Osaka, Japan.
J Biosci Bioeng. 2008 Jun;105(6):642-8. doi: 10.1263/jbb.105.642.
Toxic metal contamination in agricultural fields is an important worldwide problem. In previous studies, we developed a bioremediation system based on the symbiosis between Astragalus sinicus and the recombinant rhizobium, Mesorhizobium huakuii subsp. rengei B3 developed by overexpressing a synthetic tetrameric metallothionein gene (MTL4) and cDNA encoding the phytochelatin synthase from Arabidopsis thaliana (AtPCS). To promote the transport of metals into the nodules of the rhizobium and the accumulation of metals, the iron-regulated transporter 1 gene from A. thaliana (AtIRT1) was introduced into recombinant strain B3 containing MTL4 or AtPCS in its chromosome. The fused AtIRT1-alkaline phosphatase was expressed in the free-living recombinant rhizobium and the nodule of A. sinicus. The recombinant strain B3 carrying AtIRT1 showed a higher Cd sensitivity and a higher amount of Cd accumulated in free-living culture than the wild-type strain B3. When the recombinant strain B3 established symbiosis with A. sinicus, the introduction of AtIRT1 in the recombinant strain B3 advantaged the accumulation of Cu and As in the nodules of A. sinicus, compared with that of Cd and Zn.
农田中的有毒金属污染是一个全球性的重要问题。在先前的研究中，我们基于紫云英与重组根瘤菌中华根瘤菌华癸亚种B3之间的共生关系开发了一种生物修复系统，该重组根瘤菌是通过过表达合成的四聚体金属硫蛋白基因（MTL4）和编码拟南芥植物螯合肽合酶的cDNA（AtPCS）构建而成。为了促进金属向根瘤菌根瘤中的运输以及金属的积累，将拟南芥的铁调节转运蛋白1基因（AtIRT1）导入其染色体中含有MTL4或AtPCS的重组菌株B3中。融合的AtIRT1 - 碱性磷酸酶在自由生活的重组根瘤菌和紫云英的根瘤中表达。携带AtIRT1的重组菌株B3在自由生活培养中比野生型菌株B3表现出更高的镉敏感性和更高的镉积累量。当重组菌株B3与紫云英建立共生关系时，与镉和锌相比，重组菌株B3中AtIRT1的引入有利于紫云英根瘤中铜和砷的积累。
