Rhizosphere-induced Selenium Precipitation for Possible Applications in Phytoremediation of Se Polluted Effluents

What is it about?

Two bacterial isolates were obtained in axenic culture from the rhizosphere soil of Astragalus bisulcatus, a legume able to hyperaccumulate selenium. Both strains resulted of particular interest for their high resistance to the toxic oxyanion SeO32- (selenite, SeIV). On the basis of molecular and biochemical analyses, these two isolates were attributed to the species Bacillus mycoides and Stenotrophomonas maltophilia, respectively. Their capability in axenic culture to precipitate the soluble, bioavailable and highly toxic selenium form selenite to insoluble and relatively non-toxic Se0 (elemental selenium) was evaluated in defined medium added with 0.2 or 0.5 mm SeIV. Both strains showed to completely reduce 0.2 mm selenite in 120 h, while 0.5 mm SeIV was reduced up to 67% of the initial concentration by B. mycoides and to about 50% by S. maltophilia in 48 h. Together in a dual consortium, B. mycoides and S. maltophilia increased the kinetics of selenite reduction, thus improving the efficiency of the process. A model system for selenium rhizofiltration based on plant-rhizobacteria interactions has been proposed.

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Why is it important?

A hypothesis of technological facility is presented for the combined exploitation of hyperaccumulator plants and bacteria in the treatment of water streams containing toxic selenium oxyanions.