Characterization of a Selenium-Tolerant Rhizosphere Strain from a Novel Se-Hyperaccumulating PlantCardamine hupingshanesis

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Abstract
A novel selenium- (Se-) hyperaccumulating plant,Cardamine hupingshanesis, accumulating Se as a form of SeCys2, was discovered in Enshi, Hubei, China, which could not be explained by present selenocysteine methyltransferase (SMT) theory. However, it is interesting to investigate if rhizosphere bacteria play some roles during SeCys2accumulation. Here, one Se-tolerant rhizosphere strain,Microbacterium oxydans, was isolated fromC. hupingshanesis. Phylogenetic analysis and 16S rRNA gene sequences determined the strain as a kind of Gram positive bacillus and belonged to the familyBrevibacterium frigoritolerans. Furthermore, Se tolerance test indicated the strain could grow in extreme high Se level of 15.0 mg Se L−1. When exposed to 1.5 mg Se L−1, SeCys2was the predominant Se species in the bacteria, consistent with the Se species inC. hupingshanesis. This coincidence might reveal that this strain played some positive effect in SeCys2accumulation ofC. hupingshanesis. Moreover, when exposed to 1.5 mg Se L−1or 15.0 mg Se L−1, As absorption diminished in the logarithmic phase. In contrast, As absorption increased when exposed to 7.5 mg Se L−1, indicating As metabolism processes could be affected by Se on this strain. The present study provided a sight on the role of rhizosphere bacteria during Se accumulation for Se-hyperaccumulating plant.
Funding Information
  • National Natural Science Foundation of China (NNSFC31400091, BK2012202, 2013M540518, 1302080C)
  • Natural Science Foundation of Jiangsu Province (NNSFC31400091, BK2012202, 2013M540518, 1302080C)
  • China Postdoctoral Science Foundation (NNSFC31400091, BK2012202, 2013M540518, 1302080C)
  • Jiangsu Provincial Postdoctoral Science Foundation (NNSFC31400091, BK2012202, 2013M540518, 1302080C)

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