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United States Department of Agriculture

Agricultural Research Service

Research Project: Management Practices to Mitigate Global Climate Change, Enhance Bio-Energy Production, Increase Soil-C Stocks & Sustain Soil Productivity...

Location: Soil Plant Nutrient Research (SPNR)

Title: Pseudomonas seleniipraecipitans proteins potentially involved in selenite reduction

Author
item Hunter, William

Submitted to: Current Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 14, 2014
Publication Date: March 7, 2014
Citation: Hunter, W.J. 2014. Pseudomonas seleniipraecipitans proteins potentially involved in selenite reduction. Current Microbiology. 69:69-74.

Interpretive Summary: Selenite can be toxic in large amounts. In situ biobarriers can be used to remove this oxyanion from groundwater using a process that involves the microbial reduction of soluble selenite to insoluble elemental red selenium coupled with the retention of the precipitated elemental selenium within the barrier. However, not much is know about the biochemistry connected to this remediation process. The bacteria Pseudomonas seleniipraecipitans grows in the presence of large amounts of selenite and can reduce selenite to elemental selenium. Thus P. seleniipraecipitans may be useful as an inoculant for biobarriers designed to remove selenite from ground or surface-waters. An earlier study failed to identify the protein(s) involved in selenite reduction but this study used protein purification methods to isolate two electrophoretic gel regions, identified as bands A and B, that showed selenite-reductase-activity. Next proteomic methods were used to identify the proteins present in those regions. The enzyme glutathione reductase (GR) was detected in the A-band; and, based on this information, GR from the yeast Saccharomyces cerevisiae was purchased from a commercial source and evaluated for selenite reducing ability. The yeast GR was found to have selenite reductase activity, confirming that GR can reduce selenite to elemental selenium. In the B-band the enzyme thioredoxin reductase (ThxR) was detected and ThxR from the bacteria Escherichia coli was purchased and evaluated. The enzyme ThxR was found to have the ability to reduce selenite. Thus, evidence presented in this study shows that S. cerevisiae and P. seleniipraecipitans GR, and E. coli and P. seleniipraecipitans ThxR can all reduce selenite to elemental selenium.

Technical Abstract: Pseudomonas seleniipraecipitans grows in the presence of high levels of selenite and selenate and reduces both oxyanions to elemental selenium, a property that may make P. seleniipraecipitans useful as an inoculant for biobarriers designed to remove selenite or selenate from ground or surface-waters. An earlier study showed that P. seleniipraecipitans nitrate reductase reduced selenate to elemental selenium, but failed to identify the protein(s) involved in selenite reduction. This study used ammonium sulfate precipitation, hydrophobic interaction chromatography and native PAGE to isolate two electrophoretic gel regions, identified as bands A and B, that showed selenite-reductase-activity. Proteomics was used to identify the proteins present in those regions. Glutathione reductase (GR) was detected in the A-band; and, based on this information, Saccharomyces cerevisiae GR, obtained from a commercial source, was evaluated and found to have selenite reductase activity, confirming that GR can reduce selenite to elemental selenium. Proteomics was also used to detect the proteins present in the B-band and thioredoxin reductase (ThxR) was detected as a B-band protein; based on this information, Escherichia coli ThxR, obtained from a commercial source, was evaluated and found to have selenite-reductase-activity, confirming that ThxR can reduce selenite to elemental selenium. Thus, evidence presented in this study shows that S. cerevisiae GR and E. coli ThxR can reduce selenite to elemental selenium strongly suggests that P. seleniipraecipitans GR and ThxR can also reduce selenite to elemental selenium.

Last Modified: 7/23/2014
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