Anthyllis vulneraria/Mesorhizobium metallidurans, an efficient symbiotic nitrogen fixing association able to grow in mine tailings highly contaminated by Zn, Pb and Cd

Abstract

The excessive concentrations of toxic heavy metals in mine tailings and their very low N content make soil reclamation strategies by phytostabilization difficult. Our objective was to test if the symbiotic association between the legume Anthyllis vulneraria subsp. carpatica and the bacteria Mesorhizobium metallidurans originating from highly polluted mine tailings is able to increase N concentration in soils with contrasting Zn, Pb and Cd contents. Plants of A. vulneraria subsp. carpatica from a mine site and of a non-metallicolous subsp. praeopera from non-polluted soil were inoculated with a metallicolous or a non-metallicolous compatible Mesorhizobium spp. and grown on low and high heavy metal-contaminated soils. In contaminated soil, many nodules were observed when the metallicolous A. vulneraria was inoculated with its rhizobium species M. metallidurans, whereas the non-metallicolous A. vulneraria died after a few weeks regardless of the rhizobium inoculant. Eighty percent of the total nitrogen was derived from biological nitrogen fixation through the association between metallicolous A. vulneraria and the rhizobium grown on metal-enriched soil. The ability of the metallicolous A. vulneraria to develop a high nitrogen fixing potential opens new possibilities for promoting a low-maintenance plant cover and for stabilizing the vegetation in high heavy metal-contaminated soils

Toxic Effects of Heavy Metals on Germination and Physiological Processes of Plants

“…For example, the symbiotic association between the legume Anthyllis vulneraria subsp. carpatica and the bacterium Mesorhizobium metallidurans isolated from highly polluted mine tailings significantly increased N pool of soils heavily contaminated with zinc, lead, and cadmium (Mahieu et al 2011). Of the total soil N pool, about 80% N was due to biological nitrogen fixation (BNF) resulting from metallicolous A. vulneraria and the rhizobial interaction happening in metal-enriched soil.…”

Chemical exploitation of metal contaminated biomass produced in phytoextraction

“…In the case of nickel, previous studies showed that phytoextraction was possible with yields good enough to foresee commercial applications [18][19][20]. Latest studies on former mine sites in the South of France showed a very interesting potential [10,17] but zinc phytoextraction has not yet been subject to fi eld-scale trials.…”

“…In the South of France, former mine sites around Saint-Laurentle-Minier also host a very interesting biodiversity: the Ganges ecotype of Thlaspi Caerulescens was found to accumulate Zn at levels above 10,000 mg kg -1 [7][8][9] and Anthyllis vulneraria is a zinc hyperaccumulator legume species, which may improve contaminated soil fertility through nitrogen fi xation [10]. T. Caerulescens as well as A. Vulneraria from the Les Avinières mine site in SaintLaurent-le-Minier, France have been used in this study.…”

Improving legume nodulation and Cu rhizostabilization using a genetically modified rhizobia

“…[8] Even though, when tolerant rhizobia are present, legume nodulation in polluted soils has been observed. [10][11][12][13] The rhizoremediation process using legumes and suitable rhizosphere microorganisms can occur naturally, but it used to be slow and it can be expedited by different techniques, including biostimulation, bioaugmentation or introduction of genetically modified organisms. [14,15] Rhizosphere microorganisms have been engineered to improve their bioremediation capacities in metal contaminated soils, [16] but few works on the genetic modification of rhizobia for this purpose have been reported.…”