Some soil microbes can methylate arsenic (As) and produce dimethylarsenate (DMA) as a main product. Excessive accumulation of DMA by rice plants can cause the straighthead disease, a physiological disorder leading to substantial yield losses. DMA can also be demethylated in soil, but the mechanism and the microbes involved are not well understood. We investigated the dynamics of methylated As species, including monomethylarsenate (MMA), DMA and dimethyl-monothioarsenate (DMMTA), in three paddy soils that produced the straighthead disease. The soils were incubated under flooded conditions with or without the addition of 2-bromoethanesulfonate (BES), a specific inhibitor of methanogenesis. DMA and DMMTA concentrations in porewater increased initially as soil redox potential decreased, and then decreased rapidly coinciding with the production of methane. BES addition largely suppressed methanogenesis and the disappearance of DMA and DMMTA, but not of MMA. BES addition suppressed the transcript levels of archaeal 16S rRNA and, particularly, mcrA gene encoding methyl-coenzyme reductase subunit A. Among the core genera of archaea, the absolute abundances of Methanomassiliicoccus and Methanosarcina were decreased significantly by BES in the three soils. In a pot experiment with two soils, BES addition significantly increased DMA accumulation in rice husks and the incidence of the straighthead disease in rice. The results suggest that DMA and DMMTA demethylation in paddy soil is coupled to methanogenesis with Methanomassiliicoccus and Methanosarcina likely playing an important role.

一些土壤微生物可以甲基化砷 (As) 并产生二甲基砷酸盐 (DMA) 作为主要产物。水稻过度积累 DMA 会导致直头病，这是一种导致大量产量损失的生理疾病。DMA 也可以在土壤中脱甲基，但其机制和所涉及的微生物尚不清楚。我们研究了产生直头病害的三种稻田土壤中甲基化 As 物种的动态，包括单甲基砷酸盐 (MMA)、DMA 和单硫代砷酸二甲酯 (DMMTA)。在添加或不添加 2-溴乙磺酸盐 (BES)（一种特定的产甲烷抑制剂）的淹水条件下培养土壤。随着土壤氧化还原电位的降低，孔隙水中的 DMA 和 DMMTA 浓度最初增加，然后随着甲烷的产生而迅速下降。BES 添加在很大程度上抑制了产甲烷和 DMA 和 DMMTA 的消失，但不是 MMA。BES 添加抑制了古细菌 16S rRNA 的转录水平，特别是，编码甲基辅酶还原酶亚基A的mcrA基因。在古细菌的核心属中， BES显着降低了三种土壤中Methanomassiliicoccus和Methanosarcina的绝对丰度。在两种土壤的盆栽试验中，添加 BES 显着增加了稻壳中 DMA 的积累和水稻直头病的发病率。结果表明，稻田土壤中的 DMA 和 DMMTA 去甲基化与产甲烷作用有关，其中Methanomassiliicoccus和Methanosarcina可能起重要作用。