Identification and catalytic residues of the arsenite methyltransferase from a sulfate-reducing bacterium, Clostridium sp. BXM

Arsenic methylation is an important process frequently occurring in anaerobic environments. Anaerobic microorganisms have been implicated as the major contributors for As methylation. However, very little information is available regarding the enzymatic mechanism of As methylation by anaerobes. In t...

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Bibliographic Details
Published in:FEMS microbiology letters 2015-01, Vol.362 (1), p.1-8
Main Authors: Wang, Pei-Pei, Bao, Peng, Sun, Guo-Xin
Format: Article
Language:English
Subjects:
Anaerobes
Anaerobic environments
Anaerobic microorganisms
Anaerobic processes
Arsenic
Arsenic - metabolism
Arsenic - toxicity
Arsenite
Arsenite methyltransferase
Bacteria
Catalytic Domain
Cloning, Molecular
Clostridium
Clostridium - enzymology
Clostridium - isolation & purification
Cysteine
DNA Mutational Analysis
Drug Resistance, Bacterial
E coli
Escherichia coli - drug effects
Escherichia coli - genetics
Gene Expression
Methionine
Methylation
Methyltransferases - genetics
Methyltransferases - isolation & purification
Methyltransferases - metabolism
Microbiology
Microorganisms
Mutagenesis, Site-Directed
Recombinant Proteins - genetics
Recombinant Proteins - isolation & purification
Recombinant Proteins - metabolism
Residues
Rice fields
Site-directed mutagenesis
Soil Microbiology
Sulfate reduction
Sulfate-reducing bacteria
Sulfates
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Summary:Arsenic methylation is an important process frequently occurring in anaerobic environments. Anaerobic microorganisms have been implicated as the major contributors for As methylation. However, very little information is available regarding the enzymatic mechanism of As methylation by anaerobes. In this study, one novel sulfate-reducing bacterium isolate, Clostridium sp. BXM, which was isolated from a paddy soil in our laboratory, was demonstrated to have the ability of methylating As. One putative arsenite S-Adenosyl-Methionine methyltransferase (ArsM) gene, CsarsM was cloned from Clostridium sp. BXM. Heterologous expression of CsarsM conferred As resistance and the ability of methylating As to an As-sensitive strain of Escherichia coli. Purified methyltransferase CsArsM catalyzed the formation of methylated products from arsenite, further confirming its function of As methylation. Site-directed mutagenesis studies demonstrated that three conserved cysteine residues at positions 65, 153 and 203 in CsArsM are necessary for arsenite methylation, but only Cysteine 153 and Cysteine 203 are required for the methylation of monomethylarsenic to dimethylarsenic. These results provided the characterization of arsenic methyltransferase from anaerobic sulfate-reducing bacterium. Given that sulfate-reducing bacteria are ubiquitous in various wetlands including paddy soils, enzymatic methylation mediated by these anaerobes is proposed to contribute to the arsenic biogeochemical cycling. Arsenite methyltransferase is responsible for As methylation and volatilization in sulfate-reducing bacterium.
ISSN:1574-6968
0378-1097
1574-6968
DOI:10.1093/femsle/fnu003