Reduction of Selenite to Elemental Red Selenium by Pseudomonas sp. strain CA5

Authors: Hunter, William; Manter, Daniel

Submitted to: Current Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/25/2008
Publication Date: 2/3/2009
Citation: Hunter, W.J., Manter, D.K. 2009. Reduction of Selenite to Elemental Red Selenium by Pseudomonas sp. strain CA5. Current Microbiology. 58:493-498.

Interpretive Summary: Both natural and anthropologic activities can result the contamination of water with selenite. For example the irrigation of seleniferous soils can cause the movement of selenite into the groundwater. In addition, industrial activities, particularly those connected with the refining of sulfur-containing crude oils can cause the contamination of surface or groundwater. The occurrence of selenium oxyanions in drinking water is a health concern and the US Environmental Protection Agency has set a limit of 0.05 mg L–1 for selenium. Selenite is the most toxic of the selenium oxyanions and methods that remove it from water are needed. Biological methods that employ microorganisms to remove selenite in situ are likely the most economical approachs. We isolated and characterized a novel bacterium that is unusual in that it is highly resistance to the toxic effects of selenite. Its growth is unaffected by exposure to 64 mM selenate and it can grow at a reduced rate in the presence of 150 mM selenite. The organism reduces selenite to elemental selenium under aerobic conditions; a reduction process that effectively removes 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 a novel Pseudomonas sp. by 16S rRNA gene sequence alignment. Morphological and biochemical tests also place the organism in the genus Pseudomonas.

Technical Abstract: A Pseudomonas sp. that may be useful in bioremediation projects was isolated from soil. The strain is of potential value because it reduces selenite to elemental red selenium and is unusual in that it was resistant to high concentrations of both selenate and selenite. Cell of the strain removed 1.7 mM of selenite from the culture fluid during a seven-day incubation. No change in growth was observed when the strain was exposed to 64 mM selenate, the highest level tested. Exposure of the strain to 50, 100, and 150 mM selenite reduced growth by 28, 57, and 66%; respectively. A selenite reductase with a molecular weight of ~115 kD was detected in cell-free extracts and a protein with a molecular weight of ~700 kD was detected that reduced both selenate and nitrate. The bacterial isolate is a strict aerobe, reducing selenite to elemental red selenium under aerobic conditions only. Pseudomonas sp. strain CA5 might be useful as an inoculum for bioreactors used to harvest selenium from selenite containing groundwater. 16S rRNA gene sequence alignment and fatty acid analysis were used to identify the bacterium as a novel species of Pseudomonas related to P. argentinensis, P. flavescens and P. straminea.