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Title: Bio-reduction of Selenite to Elemental Red Selenium by Tetrathiobacter kashmirensis

Author
item Hunter, William
item Manter, Daniel

Submitted to: Current Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/28/2008
Publication Date: 7/1/2008
Citation: Hunter, W.J., Manter, D.K. 2008. Bio-reduction of Selenite to Elemental Red Selenium by Tetrathiobacter kashmirensis. Current Microbiology 57:83-88.

Interpretive Summary: The presence of selenite in water can result from natural processes or anthropologic activities. Selenite is highly mobile and irrigation of seleniferous soils can result in its movement into the groundwater. Also, industrial processes, notably those associated with the refining of sulfur-containing crude oils can cause groundwater contamination. The presence of excess selenium in drinking waters is a health concern and the US Environmental Protection Agency has set a limit of 0.05 mg L–1. Improved methods that can remove selenite from groundwater are needed. In situ biological approaches use microorganisms to remove selenite and are potentially the most economic approachs for removing many groundwater contaminants from contaminated waters. For this study we isolated, characterized, and identified a bacterium that removed excess selenite from water. The mechanism involves the biological reduction of the toxic selenite to elemental red selenium. This reduction effectively removed selenium from the water because elemental selenium is not soluble in water and is thus not available for biological uptake. This bacterium, or perhaps its enzymes or DNA, might be useful for the remediation of waters contaminated with Se oxyanions. The organism may have value as an inoculum for the in situ remediation of groundwater. The organism has been identified as Tetrathiobacter kashmirensis by 16S rRNA gene sequence alignment. Morphological and biochemical tests confirmed the gene sequence identification.

Technical Abstract: A bacterium that detoxifies selenite by reduction to insoluble elemental red selenium was isolated from soil. The strain showed an unusually high resistance to the toxic effects of selenite by growing in media containing 64 mM selenite. 16S rRNA gene sequence alignment identified the isolate as Tetrathiobacter kashmirensis. Fatty acid analysis and morphology confirmed the identification. The isolate reduced selenite to elemental selenium under aerobic conditions only. Native gel electrophoresis of cell-free extracts revealed a band, corresponding to a molecular weight of ~120 kD, which reduced selenite. In culture, the strain did not reduce selenate; however, a soluble and inducible enzyme with a molecular weight of ~ 90 kD that reduced both selenate and nitrate was present in cell-free extracts. This organism might be useful in bioreactors designed to remove selenite from contaminated water.