Environmental Microbiology Laboratory, École Polytechnique Fédérale de Lausanne , Lausanne CH-1015, Switzerland.
Laboratory for Environmental Biotechnology, École Polytechnique Fédérale de Lausanne , Lausanne CH-1015, Switzerland.
Environ Sci Technol. 2017 Sep 19;51(18):10546-10554. doi: 10.1021/acs.est.7b02970. Epub 2017 Sep 7.
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.
甲基砷（As）形态代表了在稻米中积累的砷的重要部分，而稻米中甲基砷的丰富程度存在地域模式，目前尚不清楚原因。在稻田环境中驱动砷生物甲基化的微生物，以及有利于甲基砷积累的土壤条件，尚不清楚。我们检验了这样一个假设，即在来自湄公河三角洲稻田的代谢多功能混合厌氧富集物中，硫酸盐还原菌（SRB）是砷甲基化的关键驱动因素。我们使用钼酸盐和单氟磷酸盐作为硫酸盐还原的抑制剂来评估 SRB 对砷生物甲基化的贡献，并开发了用于扩增 arsM 基因的简并引物来鉴定甲基化生物。富集培养物将 63%的亚砷酸盐转化为甲基化产物，其中二甲砷酸是主要产物。虽然钼酸盐抑制了砷的生物甲基化，但这种抑制作用与抑制硫酸盐还原无关，而是抑制了甲基化途径。基于 arsM 序列和培养物对培养基条件的生理反应，我们提出在该富集物中，氨基酸发酵生物可能是砷甲基化的潜在驱动因素。混合培养物中缺乏脱甲基能力可能促成了其强大的甲基化效率。
