Arsenic Methylation and its Relationship to Abundance and Diversity of arsM Genes in Composting Manure

Zhai, Weiwei; Wong, Mabel Ting; Luo, Fang; Hashmi, Muhammad Zaffar; Liu, Xingmei; Edwards, Elizabeth A.; Tang, Xianjin; Xu, Jianming

doi:10.1038/srep42198

Cited by 47 publications

(22 citation statements)

References 59 publications

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“…Assessments of As methylation in soils and other environments have been hindered partly by limited databases for taxonomic classification. 20,21,49 The more extensive 726 protein sequence database developed for this study, along with a primer pair having greater degeneracy to amplify a broad range of arsM sequences, has enabled a deeper examination of arsM phylogenetic diversity. This study demonstrates the utility of these new tools, in conjunction with analyses of physiological responses to As, in probing relationships between community structure and biomethylation function.…”

Section: Environmental Science and Technologymentioning

confidence: 99%

Arsenic Methylation Dynamics in a Rice Paddy Soil Anaerobic Enrichment Culture

Reid

Maillard

Bagnoud

et al. 2017

Environ. Sci. Technol.

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Methylated arsenic (As) species represent a significant fraction of the As accumulating in rice grains, and there are geographic patterns in the abundance of methylated arsenic in rice that are not understood. The microorganisms driving As biomethylation in paddy environments, and thus the soil conditions conducive to the accumulation of methylated arsenic, are unknown. We tested the hypothesis that sulfate-reducing bacteria (SRB) are key drivers of arsenic methylation in metabolically versatile mixed anaerobic enrichments from a Mekong Delta paddy soil. We used molybdate and monofluorophosphate as inhibitors of sulfate reduction to evaluate the contribution of SRB to arsenic biomethylation, and developed degenerate primers for the amplification of arsM genes to identify methylating organisms. Enrichment cultures converted 63% of arsenite into methylated products, with dimethylarsinic acid as the major product. While molybdate inhibited As biomethylation, this effect was unrelated to its inhibition of sulfate reduction and instead inhibited the methylation pathway. Based on arsM sequences and the physiological response of cultures to media conditions, we propose that amino acid fermenting organisms are potential drivers of As methylation in the enrichments. The lack of a demethylating capacity may have contributed to the robust methylation efficiencies in this mixed culture.

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Section: Environmental Science and Technologymentioning

confidence: 99%

Arsenic Methylation Dynamics in a Rice Paddy Soil Anaerobic Enrichment Culture

Reid

Maillard

Bagnoud

et al. 2017

Environ. Sci. Technol.

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“…As-methylating bacteria widely exist in As-contaminated paddy soils and rice rhizosphere ( Jia et al, 2013 ; Zhao et al, 2013 ; Zhang S.Y. et al, 2015 ; Reid et al, 2017 ), activated sludges ( Cai et al, 2013 ), contaminated aquatic ecosystems ( Desoeuvre et al, 2016 ), copper mine ( Xiao et al, 2016 ), composting manure ( Zhai et al, 2017 ), and estuarine wetland ( Zhang et al, 2017 ). It was found that there is a significant correlation between arsC and arsM genes in the paddy soils; this suggests that the two genes coexist well in the microbial As resistance system ( Zhang S.Y.…”

Section: Discussionmentioning

confidence: 99%

Microbially Mediated Methylation of Arsenic in the Arsenic-Rich Soils and Sediments of Jianghan Plain

et al. 2018

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Almost nothing is known about the activities and diversities of microbial communities involved in As methylation in arsenic-rich shallow and deep sediments; the correlations between As biomethylation and environmental parameters also remain to be elucidated. To address these issues, we collected 9 arsenic-rich soil/sediment samples from the depths of 1, 30, 65, 95, 114, 135, 175, 200, and 223 m in Jianghan Plain, China. We used microcosm assays to determine the As-methylating activities of the microbial communities in the samples. To exclude false negative results, we amended the microcosms with 0.2 mM As(III) and 20.0 mM lactate. The results indicated that the microbial communities in all of the samples significantly catalyzed arsenic methylation. The arsM genes were detectable from all the samples with the exception of 175 m, and 90 different arsM genes were identified. All of these genes code for new or new-type ArsM proteins, suggesting that new As-methylating microorganisms are widely distributed in the samples from shallow to deep sediments. To determine whether microbial biomethylation of As occurs in the sediments under natural geochemical conditions, we conducted microcosm assays without exogenous As and carbons. After 80.0 days of incubation, approximately 4.5–15.5 μg/L DMAsV were detected in all of the microcosms with the exception of that from 30 m, and 2.0–9.0 μg/L MMAsV were detected in the microcosms of 65, 114, 135, 175, 200, and 223 m; moreover, approximately 18.7–151.5 μg/L soluble As(V) were detected from the nine sediment samples. This suggests that approximately 5.3, 0, 8.1, 28.9, 18.0, 8.7, 13.8, 10.2, and 14.9% of total dissolved As were methylated by the microbial communities in the sediment samples from 1, 30, 65, 95, 114, 135, 175, 200, and 223 m, respectively. The concentrations of biogenic DMAsV show significant positive correlations with the depths of sediments, and negative correlations with the environmental NH4+ and NaCl concentrations, but show no significant correlations with other environmental parameters, such as NO3-, SO42+, TOC, TON, Fe, Sb, Cu, K, Ca, Mg, Mn, and Al. This work helps to better understand the biogeochemical cycles of arsenic in arsenic-rich shallow and deep sediments.

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“…Arsenic is biomethylated during composting of animal manures, which often contain elevated levels of As due to the use of As-containing additives to animal feed (Yang et al, 2017;Zhai et al, 2017). However, little is known about the nature of microbes involved in this process.…”

Section: Discussionmentioning

confidence: 99%

“…Arsenic speciation analysis of manure composts showed considerable amounts of methylated As species, especially dimethylarsenate (DMAs[V]) (Yang et al, 2017). DMAs(V) and, to a less extent, methylarsenate (MAs[V]), were formed during composting of manures, with the formation of methylated arsenicals being correlated with the copy number of microbial arsM genes (Zhai et al, 2017). It therefore appears that As biomethylation is an important process of As transformation during the composting process of animal manures.…”

Section: Introductionmentioning

confidence: 99%

Arsenic methylation by a novel ArsM As(III) S‐adenosylmethionine methyltransferase that requires only two conserved cysteine residues

Huang

Packianathan

et al. 2017

Molecular Microbiology

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Arsenic (As) biomethylation is an important component of the As biogeochemical cycle that can influence As toxicity and mobility in the environment. Biomethylation of As is catalyzed by the enzyme arsenite (As[III]) S-adenosylmethionine methyltransferase (ArsM). To date, all identified ArsM orthologs with As(III) methylation activities have four conserved cysteine residues, which are thought to be essential for As(III) methylation. Here, we isolated an As(III)-methylating bacterium, Bacillus sp. CX-1, and identified a gene encoding a S-adenosylmethionine methyltranserase termed BlArsM with low sequence similarities (≤ 39%) to other ArsMs. BlArsM has six cysteine residues (Cys10, Cys11, Cys145, Cys193, Cys195 and Cys268), three of which (Cys10, Cys145 and Cys195) align with conserved cysteine residues found in most ArsMs. BlarsM is constitutively expressed in Bacillus sp. CX-1. Heterologous expression of BlarsM conferred As(III) resistance. Purified BlArsM methylated both As(III) and methylarsenite (MAs[III]), with a final product of dimethylarsenate (DMAs[V]). When all six cysteines were individually altered to serine residues, only C145S and C195S derivatives lost the ability to methylate As(III) and MAs(III). The derivative C10S/C11S/C193S/C268S was still active. These results suggest that BlArsM is a novel As(III) S-adenosylmethionine methyltransferase requiring only two conserved cysteine residues. A model of As(III) methylation by BlArsM is proposed.

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Arsenic Methylation and its Relationship to Abundance and Diversity of arsM Genes in Composting Manure

Cited by 47 publications

References 59 publications

Arsenic Methylation Dynamics in a Rice Paddy Soil Anaerobic Enrichment Culture

Arsenic Methylation Dynamics in a Rice Paddy Soil Anaerobic Enrichment Culture

Microbially Mediated Methylation of Arsenic in the Arsenic-Rich Soils and Sediments of Jianghan Plain

Arsenic methylation by a novel ArsM As(III) S‐adenosylmethionine methyltransferase that requires only two conserved cysteine residues

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