In nature, the bioaccumulative potent neurotoxin methylmercury (MeHg) is produced from inorganic mercury (Hg) predominantly by anaerobic microorganisms. Hg-contaminated soils are a potential source of MeHg due to microbial activity. We examine streambank soils collected from the contaminated East Fork Poplar Creek (EFPC) in Tennessee, USA, where seasonal variations in MeHg levels have been observed throughout the year, suggesting active microbial Hg methylation. In this study, we characterized the microbial community in contaminated bank soil samples collected from two locations over a period of one year and compared the results to soil samples from an uncontaminated reference site with similar geochemistry (n = 12). Microbial community composition and diversity were assessed by 16S rRNA gene amplicon sequencing. Furthermore, to isolate potential methylators from soils, enrichment cultures were prepared using selective media. A set of three clade-specific primers targeting the gene hgcA were used to detect Hg methylators among the δ-Proteobacteria in EFPC bank soils across all seasons. Two families among the δ-Proteobacteria that have been previously associated with Hg methylation, Geobacteraceae and Syntrophobacteraceae, were found to be predominant with relative abundances of 0.13% and 4.0%, respectively. However, in soil enrichment cultures, Firmicutes were predominant among families associated with Hg methylation. Specifically, Clostridiaceae and Peptococcaceae and their genera Clostridium and Desulfosporosinus were among the ten most abundant genera with relative abundances of 2.6% and 1.7%, respectively. These results offer insights into the role of microbial communities on Hg transformation processes in contaminated bank soils in EFPC. Identifying the biogeochemical drivers of MeHg production is critical for future remediation efforts.

在自然界中，生物蓄积性有效的神经毒素甲基汞（MeHg）主要由厌氧微生物从无机汞（Hg）中产生。由于微生物的活动，汞污染的土壤是潜在的甲基汞来源。我们检查了从美国田纳西州受污染的东叉白杨溪（EFPC）收集的河岸土壤，全年都观察到MeHg水平的季节性变化，这表明微生物体内的Hg甲基化活跃。在这项研究中，我们对一年中从两个地点采集的受污染堤岸土壤样本中的微生物群落进行了表征，并将结果与​​来自具有相似地球化学的未受污染参考站点的土壤样本进行了比较（n = 12）。通过16S rRNA基因扩增子测序评估微生物群落组成和多样性。此外，为了从土壤中分离出潜在的甲基化剂，使用选择性培养基制备了富集培养物。一组针对基因hgcA的三种进化枝特异性引物被用于检测EFPC库土中所有季节的δ-变形杆菌中的Hg甲基化子。先前发现与Hg甲基化有关的δ-变形杆菌中有两个家族，相对丰富度分别为0.13％和4.0％。但是，在土壤富集培养中，与汞甲基化有关的家庭中主要是硬毛虫。具体而言，梭菌科和肽球菌科及其梭菌属和Desulfosporosinus是十个最丰富的属为分别为2.6％和1.7％，相对丰度之间。这些结果提供了对EFPC污染河岸土壤中微生物群落在汞转化过程中的作用的见解。识别甲基汞生产的生物地球化学驱动因素对于未来的修复工作至关重要。