Contamination of rice by the potent neurotoxin methylmercury (MeHg) originates from microbe-mediated Hg methylation in soils. However, the high diversity of Hg methylating microorganisms in soils hinders the prediction of MeHg formation and challenges the mitigation of MeHg bioaccumulation via regulating soil microbiomes. Here we explored the roles of various cropland microbial communities in MeHg formation in the potentials leading to MeHg accumulation in rice and reveal that Geobacteraceae are the key predictors of MeHg bioaccumulation in paddy soil systems. We characterized Hg methylating microorganisms from 67 cropland ecosystems across 3,600 latitudinal kilometres. The simulations of a rice-paddy biogeochemical model show that MeHg accumulation in rice is 1.3–1.7-fold more sensitive to changes in the relative abundance of Geobacteraceae compared to Hg input, which is recognized as the primary parameter in controlling MeHg exposure. These findings open up a window to predict MeHg formation and accumulation in human food webs, enabling more efficient mitigation of risks to human health through regulations of key soil microbiomes.

强效神经毒素甲基汞（MeHg）对水稻的污染源于土壤中微生物介导的汞甲基化。然而，土壤中汞甲基化微生物的高度多样性阻碍了甲基汞形成的预测，并对通过调节土壤微生物组缓解甲基汞生物积累提出了挑战。在这里，我们探讨了各种农田微生物群落在甲基汞形成中的作用，以及导致水稻中甲基汞积累的潜力，并揭示了地杆菌科是水稻土系统中甲基汞生物积累的关键预测因子。我们对跨纬度 3,600 公里的 67 个农田生态系统的汞甲基化微生物进行了特征分析。稻田生物地球化学模型的模拟表明，与汞输入相比，水稻中甲基汞积累对地杆菌科相对丰度变化的敏感度高1.3-1.7倍，汞输入被认为是控制甲基汞暴露的主要参数。这些发现为预测人类食物网中甲基汞的形成和积累打开了一个窗口，从而可以通过对关键土壤微生物组的调节来更有效地减轻对人类健康的风险。