Enhancement of metal phytostabilization by inoculation of endophytic bacterium Achromobacter piechaudii E6S

Application of hyperaccumulator–endophyte symbiotic system is becoming a potential technique to improve phytostabilization. The objective was to isolate metal resistant and immobilizing endobacterium and to evaluate its role... [ view full abstract ]

Application of hyperaccumulator–endophyte symbiotic system is becoming a potential technique to improve phytostabilization. The objective was to isolate metal resistant and immobilizing endobacterium and to evaluate its role in enhancing plant growth and metal phytostabilization. A metal resistant endophytic bacterial strain E6S was isolated from stems of Sedum plumbizincicola using DF salts minimal agar medium with 1-aminocyclopropane-1-carboxylate (ACC) as sole nitrogen source and identified based on morphological, biochemical characteristics, partial 16S rDNA sequence and phylogenetic analysis. Metal resistance and sensitivity to antibiotics of E6S were determined by plate dilution and disc diffusion method, respectively. Plant beneficial traits of E6S, e.g. phosphate (P) solubilization and indole-3-acetic acid (IAA) production were measured in Pikovskayas and Luria–Bartani medium, respectively. The ability of E6S to immobilize metals in soil and to absorb metal ions by its cells in liquid media were also analysed. The effects of E6S on the growth and metal accumulation in S. plumbizincicola were assessed in pot experiment. Strain E6S exhibited high level resistance to various metals (Cd, Zn, Pb) and antibiotics (ampicillin, chloramphenicol, kanamycin, tetracycline and streptomycin). Besides utilizing ACC, E6S was able to solubilize P and produce IAA. Inoculation of E6S significantly decreased concentrations of bioavailable Cd, Zn and Pb. In addition, E6S bound considerable amounts of metal ions in their resting cells in the sequence: Zn ˃ Cd ˃ Pb. Inoculation of E6S stimulated plant biomass, uptake and bioconcentration factor of Cd, Zn and Pb. However, E6S significantly declined translocation factor of Cd and Zn less than 1.