Rhizobacterial effects on nickel extraction from soil and uptake by Alyssum murale

Alyssum murale has a remarkable ability to hyperaccumulate Ni from soils containing mostly nonlabile Ni. Here, rhizobacteria are shown to play an important role in increasing the availability of Ni in soil, thus enhancing Ni accumulation by A. murale . Three bacteria, originally isolated from the rhizosphere of A. murale , were examined for their ability to solubilize Ni in soil and for their effect on Ni uptake into Alyssum . Sphingomonas macrogoltabidus , Microbacterium liquefaciens , and Microbacterium arabinogalactanolyticum were added to both sterile and nonsterile Ni-rich Serpentine soil from OR, USA. Sphingomonas macrogoltabidus significantly reduced Ni extraction by 10 mM Sr(NO3 )(2) from soil, M. arabinogalactanolyticum significantly increased Ni extraction, whereas M. liquefaciens had no effect. Extractability of few other metals was affected by inoculation. When these bacteria were added to surface-sterilized seeds of A. murale grown in nonsterile soil, they increased Ni uptake into the shoot by 17% (S. macrogoltabidus ), 24% (M. liquefaciens ), and 32.4% (M. arabinogalactanolyticum ), compared with uninoculated controls. These results show that bacteria are important for Ni uptake, which from a commercial perspective, could significantly increase revenue generated during phytomining of Ni from soil.