A novel bioremediation system for heavy metals using the symbiosis between leguminous plant and genetically engineered rhizobia.
A novel plant-bacterial remediation system for heavy metals (HM) was developed by expression of tetrameric human metallothionein (MTL4) in Mesorhizobium huakuii subsp. rengei B3, a strain which infects and forms nodules on a green manure, Astragalus sinicus. The MTL4 gene was fused to the nifH and nolB promoters, which generated nodule- specific expression of the MTL4 gene. The expression analysis of the MTL4 gene was demonstrated in free-living cells in the presence of Cd(2+) and Cu(2+), under the low oxygen condition. The MTL4 under the nifH and nolB promoters was expressed and increased the accumulation of Cd(2+), but not Cu(2+) in free-living cells. The expression of the integrated nifH-MTL4 gene in the chromosome of strain B3 was also expressed stably and accumulated Cd(2+) in the bacterial cells. The MTL4 transcripts were detected by in situ hybridization in bacteroids of mature nodules of A. sinicus containing nifH-MTL4 and nolB-MTL4 fusion gene. Moreover the MTL4 protein was detected by immunostaining. By infection of the recombinant B3, A. sinicus established symbiosis with the recombinant B3 that was grown in Cd(2+) and Cu(2+)-polluted soils. The symbionts increased Cd(2+) accumulation in nodules 1.7-2.0-fold, whereas, no significantly increase in Cu(2+) accumulation was noted.
Sriprang
Rutchadaporn
R
Department of Biotechnology, Graduate School of Engineering, Osaka University, 2-1 Yamada-oka, Suita-shi, Osaka 565-0871, Japan.
Hayashi
Makoto
M
Yamashita
Mitsuo
M
Ono
Hisayo
H
Saeki
Kazuhiko
K
Murooka
Yoshikatsu
Y
D027883:Astragalus Plant / Q000378:metabolism* / Q000382:microbiology*; D001673:Biodegradation, Environmental; D015964:Gene Expression Regulation, Bacterial; D024861:Genetic Enhancement / Q000379:methods; D006801:Humans; D008668:Metallothionein / Q000235:genetics / Q000378:metabolism; D019216:Metals, Heavy / Q000302:isolation & purification / Q000378:metabolism*; D018517:Plant Roots / Q000378:metabolism / Q000382:microbiology; D015202:Protein Engineering / Q000379:methods*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D015203:Reproducibility of Results; D012230:Rhizobiaceae / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D012680:Sensitivity and Specificity; D012989:Soil Pollutants / Q000302:isolation & purification / Q000378:metabolism; D013045:Species Specificity; D013559:Symbiosis / Q000502:physiology; D018505:Waste Management / Q000379:methods*
D019216:Metals, Heavy; D011994:Recombinant Proteins; D012989:Soil Pollutants; D008668:Metallothionein