Arsenite S-Adenosylmethionine Methyltransferase Is Responsible for Antimony Biomethylation in Nostoc sp. PCC7120

Abstract

Antimony (Sb) biomethylation is an important but uninformed process in Sb biogeochemical cycling. Methylated Sb species have been widely detected in the environment, but the gene and enzyme for Sb methylation remain unknown. Here, we found that arsenite S-adenosylmethionine methyltransferase (ArsM) is able to catalyze Sb(III) methylation. The stepwise methylation by ArsM forms mono-, di-, and trimethylated Sb species. Sb(III) is readily coordinated with glutathione, forming the preferred ArsM substrate which is anchored on three conserved cysteines. Overexpressing arsM in Escherichia coli AW3110 conferred resistance to Sb(III) by converting intracellular Sb(III) into gaseous methylated species, serving as a detoxification process. Methylated Sb species were detected in paddy soil cultures, and phylogenetic analysis of ArsM showed its great diversity in ecosystems, suggesting a high metabolic potential for Sb(III) methylation in the environment. This study shows an undiscovered microbial process methylating aqueous Sb(III) into the gaseous phase, mobilizing Sb on a regional and even global scale as a re-emerging contaminant.

Antimony Release and Volatilization from Organic-Rich and Iron-Rich Submerged Soils

“…Soluble methylated pentavalent Sb species (mono-, di-and tri-methylated Sb species (soluble MMSb V , DMSb V , and TMSb V , respectively)) are the products of microbial methylation. The reduced volatile species, trimethylstibine ((CH 3 ) 3 Sb), is proposed as the Sb methylation end product [60][61][62][63]. Other volatile hydride Sb species (called stibines), such as stibine (SbH 3 ), monomethyl-and dimethyl-stibines, have also been detected in the headspace gases of microbial incubations [53,64,65].…”