Submitted to: Current Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 9, 2006
Publication Date: May 1, 2007
Citation: Hunter, W.J. 2007. An Azospira oryzae (syn Dechlorosoma suillum) Strain the Reduces Selenate and Selenite to Elemental Red Selenium. Current Microbiology. 54: 376-381. Interpretive Summary: Selenate and selenite are naturally occurring compounds, sometimes present in irrigation and drinking waters, which can be toxic to humans and animals if ingested in excess amounts. Methods that can remove excess selenate and selenite from contaminated waters are needed and in situ biological approaches that use microorganisms to remove the selenite are potentially the most economic. We isolated, characterized, and identified a bacterium that removes selenite from flowing water and that may be useful for the in situ remediation of groundwater. The organism has been identified as Azospira oryzae by morphological and biochemical tests and by 16S rRNA gene sequence alignment. The mechanism involves the biological reduction of the toxic selenium compounds to elemental red selenium. Elemental selenium is not soluble in water and is thus not a groundwater contaminant. This bacterium, or perhaps its enzymes or DNA, might be useful for the remediation of waters contaminated with Se oxyanions.
Technical Abstract: A bacterium that reduces the soluble selenium oxyanions, selenate and selenite, to insoluble elemental red selenium (Se0) was isolated from a laboratory reactor developed to remove selenate from groundwater. Gene sequence alignment of the 16S rRNA allowed identification of the isolate as Azospira oryzae. Biochemical and morphological characterization confirm the identification. The isolate reduces selenate and selenite to Se0 under microaerophilic and denitrifying conditions but not under aerobic conditions. It does not use selenate or selenite as terminal e' donors. Se oxyanion reduction causes the formation of Se nanospheres that are 0.025 ± 0.004 µm in diameter. Nanospheres maybe associated with the cells or free in the medium. The activity that is associated with the reduction of selenate has a molecular mass of about 500 kD and the activity associated with the reduction of selenite has a mass of about 55 kD. Selenite reduction was inhibited by tungsten. The molecular masses of these activities were different from those associated with the reduction of dimethylsulfoxide, sulfate, and nitrite. This bacterium, or perhaps its enzymes or DNA, might be useful for the remediation of waters contaminated with Se oxyanions.