Characterization of root-nodule bacteria isolated from Hedysarum spinosissimum L, growing in mining sites of Northeastern region of Morocco

The aim of this study was to identify bacteria present in the nodules of the legume Hedysarum spinosissimum growing in metal-contaminated soils; and to test whether these root-nodule bacteria are able to promote host plant growth and enhance their phytostabilization potential. Seventy-four bacteria were isolated from nodules of H. spinosissimum growing in 3 different mining sites in Morocco and were identified by 16S rDNA gene sequencing. They belonged to 8 genera affiliated to Pseudomonas (49 strains), Pantoea (11), Rhizobium (6), Herbaspirillum (3), Bacillus (2), and one strain of Serratia, Agrobacterium and Azospirillum. Seven strains, presenting a high tolerance to Zn and Pb, exhibited capacity of inorganic phosphate solubilization and ammonia production from peptone degradation. The inoculation of H. spinosissimum, growing in 2000 µM of Zn by Pseudomonas putida and Herbaspirillum huttiense suppresses Zn toxicity symptoms in plants and also enhances plant growth by significantly increasing plant shoot and root fresh weights. The maximal Zn accumulation was observed in roots of plants inoculated by Pseudomonas putida with a translocation factor of 0.05(± 0.006). Our results, evidence that the selection of metal-resistant bacteria is a key step in polluted soils for the use of plants like Hedysarum spinosissimum for in situ phytoremediatio