REDUCTION OF SELENITE TO ELEMENTAL SELENIUM BY A BACTERIAL STRAIN OF Stenotrophomonas sp. ISOLATED FROM THE RHIZOSPHERE OF THE HYPERACCUMULATOR LEGUME Astragalus bisulcatus

摘要

The excess of selenium (Se) in soils and water bodies may create environmental risks and health hazards for either animals or humans. Nowadays, one of the most promising approaches to the decontamination of Se polluted soils seems to be the recourse to plant-based techniques referred to as phytoremediation. The aim of this study was to evaluate the capability of reducing water-soluble and toxic Se oxyanions, namely selenite (SeIV) and selenate (SeVI), to less toxic and water-insoluble elemental selenium (Se0) by particular bacteria colonising the rhizosphere of plants which hyperaccumulate Se. Evaluating such a peculiar microbial activity within plant roots/microbes systems might result of outmost importance for designing Se decontamination protocols, with a special attention to phytostabilisation mechanisms. Bacterial distribution in the rhizosphere of the hyperaccumulator legume Astragalus bisulcatus has been depicted by means of DGGE (denaturing gradient gel electrophoresis) analysis, while a classical culture-based approach was adopted for the axenic isolation of rhizospheric bacteria capable of reducing SeIV and SeVI to Se0. One of the bacterial isolates was taxonomically assigned to Stenotrophomonas sp.. It has been shown as particularly resistant to selenite on the basis of an estimated minimal inhibitory concentration (MIC) for SeIV up to 50 mM. A net efficiency in reducing SeIV to Se0 has been also evidenced in this strain whose such a worth capacity is here reported.