posted on 2024-01-05, 16:35authored byJianwei Li, Zhipeng Yin, Kun Xu, Li Yan, Li Ye, Jingjing Du, Chuanyong Jing, Jianbo Shi
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.