Bifunctional protein ArsRM contributes to arsenite methylation and resistance in Brevundimonas sp. M20

Abstract Background Arsenic (As) with various chemical forms is the most prevalent water and environmental toxin. This metalloid occurs worldwide and causes various diseases including cancer, especially arsenite [As(III)]. Organification of arsenite is an effective way for organisms to cope with arsenic toxicity. Microbial communities have been shown to be a vital contributor in the global arsenic biocycle and to be a promising way to reduce arsenite toxicity. Methods Brevundimonas sp M20 with arsenite resistance was isolated from aquaculture sewage. arsHRNBC cluster and the metRFHH operon of M20 was identified by sequencing. Gene of ArsR/methyltransferase fusion protein, arsRM, was amplified and expressed in Escherichia coli BL21 (DE3) and resistance to arsenic was determined in present of 0.25–6 mM As(III), As(V), or Rox(V). Methylation and regulatory details of ArsRM were analyzed by Discovery Studio 2.0. Then methyltransferase activity analysis and EMSAs confirmed the functions. Results MIC of Brevundimonas sp. M20 to arsenite is 4.5 mM. A 3,011-bp arsenite resistant ars cluster arsHRNBC and a 5649-bp methionine biosynthesis met operon were found on the 3.315-Mb chromosome. Transcriptional regulator/methyltransferase fusion protein ArsRM is a difunctional protein. Expression of ArsRM in E. coli increased arsenite resistant to 1.5 mM. Arsenite methylation and binding to its own promoter region was confirmed by ArsRM. The As(III)-binding site (ABS) and SAM-binding motif provide the difunctional characteristic to ArsRM. Conclusions We conclude that ArsRM promotes the arsenite methylation and binding of to its own promoter region. This difunctional characteristic directly connects methionine and arsenic metabolism. Our findings add important knowledge about microbial arsenic resistance and detoxification. Future work should further explore the regulatory mechanism of ArsRM on met operon and ars cluster.