19 September 2014
Bioaccumulation of Cd 2+ in soil bacteria might represent an important route of metal transfer to associated mycorrhizal fungi and plants and may have potential as a tool to accelerate Cd 2+ extraction in the bioremediation of contaminated soils. The present study examined the bioaccumulation of Cd 2+ in 15 bacterial strains representing three phyla ( Firmicutes, Proteobacteria, and Bacteroidetes) that were isolated from the rhizosphere, ectomycorrhizae, and fruitbody of ectomycorrhizal fungi. The strains Pseudomonas sp. IV-111-14, Variovorax sp. ML3-12, and Luteibacter sp. II-116-7 displayed the highest biomass productivity at the highest tested Cd 2+ concentration (2 mM). Microscopic analysis of the cellular Cd distribution revealed intracellular accumulation by strains Massilia sp. III–116-18, Pseudomonas sp. IV-111-14, and Bacillus sp. ML1-2. The quantities of Cd measured in the interior of the cells ranged from 0.87 to 1.31 weight % Cd. Strains originating from the rhizosphere exhibited higher Cd 2+ accumulation efficiencies than strains from ectomycorrhizal roots or fruitbodies. The high Cd tolerances of Pseudomonas sp. IV-111-16 and Bacillus sp. ML1-2 were attributed to the binding of Cd 2+ as cadmium phosphate. Furthermore, silicate binding of Cd 2+ by Bacillus sp. ML1-2 was observed. The tolerance of Massilia sp. III-116-18 to Cd stress was attributed to a simultaneous increase in K + uptake in the presence of Cd 2+ ions. We conclude that highly Cd-tolerant and Cd-accumulating bacterial strains from the genera Massilia sp., Pseudomonas sp., and Bacillus sp. might offer a suitable tool to improve the bioremediation efficiency of contaminated soils.