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Respiratory selenite reductase from Bacillus selenitireducens strain MLS10

March 13, 2019

The putative respiratory selenite [Se(IV)] reductase (Srr) from Bacillus selenitireducens MLS10 has been identified through a polyphasic approach involving genomics, proteomics, and enzymology. Nondenaturing gel assays were used to identify Srr in cell fractions, and the active band was shown to contain a single protein of 80 kDa. The protein was identified through liquid chromatography-tandem mass spectrometry (LC-MS/MS) as a homolog of the catalytic subunit of polysulfide reductase (PsrA). It was found to be encoded as part of an operon that contains six genes that we designated srrE, srrA, srrB, srrC, srrD, and srrF. SrrA is the catalytic subunit (80 kDa), with a twin-arginine translocation (TAT) leader sequence indicative of a periplasmic protein and one putative 4Fe-4S binding site. SrrB is a small subunit (17 kDa) with four putative 4Fe-4S binding sites, SrrC (43 kDa) is an anchoring subunit, and SrrD (24 kDa) is a chaperon protein. Both SrrE (38 kDa) and SrrF (45 kDa) were annotated as rhodanese domain-containing proteins. Phylogenetic analysis revealed that SrrA belonged to the PsrA/PhsA clade but that it did not define a distinct subgroup, based on the putative homologs that were subsequently identified from other known selenite-respiring bacteria (e.g., Desulfurispirillum indicum and Pyrobaculum aerophilum). The enzyme appeared to be specific for Se(IV), showing no activity with selenate, arsenate, or thiosulfate, with a Km of 145 ± 53 μM, a Vmax of 23 ± 2.5 μM min−1, and a kcat of 23 ± 2.68 s−1. These results further our understanding of the mechanisms of selenium biotransformation and its biogeochemical cycle.

Publication Year 2019
Title Respiratory selenite reductase from Bacillus selenitireducens strain MLS10
DOI 10.1128/JB.00614-18
Authors Michael L. Wells, Jennifer McGarry, Maissa M Gaye, Partha Basu, Ronald S. Oremland, John F. Stolz
Publication Type Article
Publication Subtype Journal Article
Series Title Journal of Bacteriology
Index ID 70215597
Record Source USGS Publications Warehouse
USGS Organization WMA - Earth System Processes Division