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.