Microbial arsenic (As) methylation in paddy soil produces mainly dimethylarsenate (DMA), which can cause physiological straighthead disease in rice. The disease is often highly patchy in the field, but the reasons remain unknown. We investigated within-field spatial variations in straighthead disease severity, As species in rice husks and in soil porewater, microbial composition and abundance of arsM gene encoding arsenite S-adenosylmethionine methyltransferase in two paddy fields. The spatial pattern of disease severity matched those of soil redox potential, arsM gene abundance, porewater DMA concentration, and husk DMA concentration in both fields. Structural equation modelling identified soil redox potential as the key factor affecting arsM gene abundance, consequently impacting porewater DMA and husk DMA concentrations. Core amplicon variants that correlated positively with husk DMA concentration belonged mainly to the phyla of Chloroflexi, Bacillota, Acidobacteriota, Actinobacteriota, and Myxococcota. Meta-omics analyses of soil samples from the disease and non-disease patches identified 5129 arsM gene sequences, with 71% being transcribed. The arsM-carrying hosts were diverse and dominated by anaerobic bacteria. Between 96–115 arsM sequences were significantly more expressed in the soil samples from the disease than from the non-disease patch, which were distributed across 18 phyla, especially Acidobacteriota, Bacteroidota, Verrucomicrobiota, Chloroflexota, Pseudomonadota, and Actinomycetota. This study demonstrates that even a small variation in soil redox potential within the anoxic range can cause a large variation in the abundance of As-methylating microorganisms, thus resulting in within-field variation in rice straighthead disease. Raising soil redox potential could be an effective way to prevent straighthead disease.

中文翻译：

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土壤氧化还原状态控制微生物砷甲基化和水稻直头病的田间空间变化

水稻土中微生物砷（As）甲基化主要产生二甲基砷酸盐（DMA），可引起水稻生理性直头病。这种疾病在田间的分布通常非常分散，但原因仍不清楚。我们研究了两块稻田中直头病严重程度、稻壳和土壤孔隙水中砷种类、微生物组成和编码亚砷酸 S-腺苷甲硫氨酸甲基转移酶的 arsM 基因的田内空间变化。两个田地中疾病严重程度的空间模式与土壤氧化还原电位、arsM 基因丰度、孔隙水 DMA 浓度和谷壳 DMA 浓度的空间模式相匹配。结构方程模型确定土壤氧化还原电位是影响 arsM 基因丰度的关键因素，从而影响孔隙水 DMA 和谷壳 DMA 浓度。与果壳 DMA 浓度呈正相关的核心扩增子变异主要属于 Chloroflexi、Bacillota、Acidobacteriota、Actinobacteriota 和 Myxococcota 门。对病斑和非病斑土壤样本进行元组学分析，确定了 5129 个 arsM 基因序列，其中 71% 已转录。携带arsM的宿主多种多样，且以厌氧菌为主。 96-115 arsM 序列在病害土壤样本中的表达量显着高于非病害斑块，这些序列分布在 18 个门，特别是酸杆菌门、拟杆菌门、疣微菌门、绿曲菌门、假单胞菌门和放线菌门。这项研究表明，即使缺氧范围内土壤氧化还原电位的微小变化也会导致砷甲基化微生物丰度的巨大变化，从而导致水稻直头病的田间变异。提高土壤氧化还原电位可能是预防直头病的有效方法。