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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: A rhizobium selenitireducens protein showing selenite reductase activity

Author
item Hunter, William

Submitted to: Current Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 28, 2013
Publication Date: October 25, 2013
Citation: Hunter, W.J. 2013. A rhizobium selenitireducens protein showing selenite reductase activity. Current Microbiology. 68:311-316.

Interpretive Summary: Research has shown that in situ biobarriers can remove the sometimes toxic metalloid selenite (SeO3–2) from groundwater. The process involves the microbial reduction of the soluble SeO3–2 anion to insoluble elemental red selenium (Se0) and the subsequent retention of the precipitated Se0 within the biobarrier. The biochemistry associated with this bioremediation process is poorly understood. Within the bacterium Rhizobium selenitireducens at least two enzymes are potentially involved; one, a nitrite-reductase has been shown to reduce SeO3–2 to Se0 but other enzymes may also be involved. This study investigated a second enzyme that might be involved in this process. Proteins from R. selenitireducens cells were extracted from the cells and run on native electrophoresis gels. When these gels were incubated with NADH and SeO3–2 a band of precipitated Se0 developed signifying the presence of a SeO3–2 reducing enzyme. The activity bands were cut from the gel and analyzed via LCMSMS. The amino acid sequences associated with the SeO3–2 reducing enzyme indicated the presence of an NADH:flavin oxidoreductase that resembles a protein from Sinorhizobium medicae. The protein is part of a protein family termed old-yellow-enzymes (OYE) that contain a flavin binding site. OYE enzymes are often involved in protecting cells from oxidative stress and are generally active on a wide range of substrates. This report is the first to suggest the involvement of an OYE enzyme in SeO3–2 reduction.

Technical Abstract: Biobarriers remove, via precipitation, the metalloid selenite (SeO3–2) from groundwater; a process that involves the biological reduction of soluble SeO3–2 to insoluble elemental red selenium (Se0). The enzymes associated with this reduction process are poorly understood. In Rhizobium selenitireducens at least two enzymes are potentially involved; one, a nitrite-reductase reduces SeO3–2 to Se0 but another protein may also be involved; this study investigated that protein. Proteins from R. selenitireducens cells were precipitated with ammonium sulfate and run on native electrophoresis gels. When these gels were incubated with NADH and SeO3–2 a band of precipitated Se0 developed signifying the presence of a SeO3–2 reducing protein. Bands were cut from the gel and analyzed for peptides via LCMSMS. The amino acid sequences associated with the bands indicated the presence of an NADH:flavin oxidoreductase that resembles YP_001326930 from Sinorhizobium medicae. The protein is part of a protein family termed old-yellow-enzymes (OYE) that contain a flavin binding domain. OYE enzymes are often involved in protecting cells from oxidative stress and, due in part to an active site that has a highly accessible binding pocket, are generally active on a wide range of substrates. This report is the first of an OYE enzyme being involved in SeO3–2 reduction.

Last Modified: 12/19/2014
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