Isolation and characterization endophytic bacteria from hyperaccumulator Sedum alfredii Hance and their potential to promote phytoextraction of zinc polluted soil

The aim of this study was to isolate and characterize endophytic bacteria from roots, stems and leaves of Zn/Cd hyperaccumulator Sedum alfredii. Endophytic bacteria were observed in roots, stems and leave of S. alfredii, with a significantly higher density in roots, followed by leave and stems. A total of fourteen bacterial endophytes were isolated and are closely related phylogenetically to Pseudomonas, Bacillus, Stenotrophomonas, Acinetobacte by 16S rRNA sequence analysis. Most of the endophytic bacteria were found to exhibit high Zn and Cd resistance characteristics, but difference existed among this isolates. The fourteen endophytic bacteria all had the capacity to produce IAA. Moreover, strains VI₈L₁, VI₈L₂, VI₈L₄, VI₈R₂, VI₈R₃ and II₂R₃ could solubilize Ca₃(PO₄)₂, strains VI₈L₂, II₈L₄ and VI₈R₂ could produce siderophore, and strains VI₈L₂ and VI₈R₃ had the capacity of nitrogen fixation. Both plate and broth assay proved that strain VI₈L₁, VI₈L₂, II₈L₄ and VI₈R₂ were able to effectively solubilize ZnCO₃ and Zn₃(PO₄)₂. The filtrate liquid media after growth of strains VI₈L₁, VI₈L₂, II₈L₄ and VI₈R₂ extracted much higher Zn from artificially ZnCO₃ and Zn₃(PO₄)₂ contaminated soils than those extracted by axenic SMS broth, and the filtrates of the culture media supporting growth of strains VI₈L₂, II₈L₄ and VI₈R₂ also extracted significantly greater quantities of Zn from the Dabaoshan contaminated soils. This Zn mobilizing, plant growth promoting and metal resistant endophytic bacteria may offer promise as inoculants to increase soil Zn bioavailability and improve growth and Zn accumulation by S. alfredii.