RESUMEN
Co-evolution of plant beneficial microbes in contaminated environments enhances plant growth and mitigates abiotic stress. However, few studies on heavy metal (HM) tolerant plant growth-promoting bacteria (PGPB) promoting crop growth in Morocco's farming areas affected by drought and salinity are available. Plant associated bacteria tolerant to HM and able to produce indole acetic acid and siderophores, display ACC-deaminase activity and solubilize phosphate, were isolated from long-term metal exposed environments. Tolerance to HM and biofilms formation in the absence or presence of HM were assessed. A consortium including two Ensifer meliloti strains (RhOL6 and RhOL8), one Pseudomonas sp. strain (DSP17), and one Proteus sp. strain (DSP1), was used to inoculate alfalfa (Medicago sativa) seedlings under various conditions, namely, salt stress (85 mM) and water stress (30% water holding capacity). Shoot and root dry weights of alfalfa were measured 60 days after sowing. In the presence of HM, DSP17 showed the greatest auxin production, whereas RhOL8 had the highest ACC-deaminase activity and DSP17 formed the densest biofilm. Root dry weight increased 138% and 195% in salt and water stressed plants, respectively, regarding non-inoculated controls. Our results confirm the improvement of alfalfa growth and mitigation of salt and drought stress upon inoculation.
Asunto(s)
Medicago sativa , Metales Pesados , Medicago sativa/microbiología , Medicago sativa/crecimiento & desarrollo , Bacterias/aislamiento & purificación , Bacterias/clasificación , Bacterias/genética , Bacterias/crecimiento & desarrollo , Ácidos Indolacéticos/metabolismo , Microbiología del Suelo , Estrés Salino , Raíces de Plantas/microbiología , Raíces de Plantas/crecimiento & desarrollo , Marruecos , Sequías , Contaminantes del Suelo , Biopelículas/crecimiento & desarrollo , Estrés Fisiológico , Liasas de Carbono-Carbono/metabolismoRESUMEN
Soil and mine tailings are unreceptive to plant growth representing an imminent threat to the environment and resource sustainability. Using indigenous plants and their associated rhizobacteria to restore mining sites would be an eco-friendly solution to mitigate soil-metal toxicity. Soil prospection from Draa Sfar and Kettara mining sites in Morocco was carried out during different seasons for native plant sampling and rhizobacteria screening. The sites have been colonized by fifteen tolerant plant species having different capacities to accumulate Cu, Zn, and P in their shoots/root systems. In Draa Sfar mine, Suaeda vera J.F. Gmel., Sarcocornia fruticosa (L.) A.J. Scott., and Frankenia corymbosa Desf. accumulated mainly Cu (more than 90 mg kg-1), Atriplex halimus L. accumulated Zn (mg kg-1), and Frankenia corymbosa Desf. accumulated Pb (14 mg kg-1). As for Kettara mine, Aizoon canariense L. mainly accumulated Zn (270 mg kg-1), whereas Forsskalea tenacissima L. was the best shoot Cu accumulator with up to 50 mg kg-1, whereas Cu accumulation in roots was 21 mg kg-1. The bacterial screening revealed the strains' abilities to tolerate heavy metals up to 50 mg kg-1 Cu, 250 mg kg-1 Pb, and 150 mg kg-1 Zn. Isolated strains belonged mainly to Bacillaceae (73.33%) and Pseudomonadaceae (10%) and expressed different plant growth-promoting traits, alongside their antifungal activity. Results from this study will provide an insight into the ability of native plants and their associated rhizobacteria to serve as a basis for remediation-restoration strategies.
Asunto(s)
Metales Pesados , Contaminantes del Suelo , Bacterias , Biodegradación Ambiental , Monitoreo del Ambiente , Metales Pesados/análisis , Marruecos , Raíces de Plantas/química , Suelo , Contaminantes del Suelo/análisisRESUMEN
Accumulation of high concentrations of heavy metals in environments can cause many human health risks and serious ecological problems. Nowadays, bioremediation using microorganisms is receiving much attention due to their good performance. The aim of this work is to investigate heavy metals resistance and bioaccumulation potential of actinobacteria strains isolated from some abandoned mining areas. Analysis of mining residues revealed that high concentration of zinc "Zn" was recorded in Sidi Bouatman, Arbar, and Bir Nhass mining residues. The highest concentration of lead "Pb" was found in Sidi Bouatman. Copper "Cu," cadmium "Cd," and chromium "Cr" were found with moderate and low concentrations. The resistance of 59 isolated actinobacteria to the five heavy metals was also determined. Using molecular identification 16S rRNA, these 27 isolates were found to belong to Streptomyces and Amycolatopsis genera. The results showed different levels of heavy metal resistance; the minimum inhibitory concentration (MIC) recorded was 0.55 for Pb, 0.15 for Cr, and 0.10 mg·mL(-1) for both Zn and Cu. Chemical precipitation assay of heavy metals using hydrogen sulfide technic (H2S) revealed that only 27 isolates have a strong ability to accumulate Pb (up to 600 mg of Pb per g of biomass for Streptomyces sp. BN3).