The effects of long-term rare earth element (REE) and heavy metal (HM) contamination on soil bacterial communities remains poorly understood. In this study, soil samples co-contaminated with REEs and HMs were collected from a rare-earth tailing dam. The bacterial community composition and diversity were analyzed through Illumina high-throughput sequencing with 16S rRNA gene amplicons. Bacterial community richness and diversity were lower in the co-contaminated soils than in the uncontaminated soils, with clearly different bacterial community compositions. The results showed that total organic carbon and available potassium were the most important factors affecting bacterial community richness and diversity, followed by the REE and HM contents. Although the canonical correspondence analysis results showed that an REE alone had no obvious effects on bacterial community structures, we found that the combined effects of soil physicochemical properties and REE and HM contents regulated bacterial community structure and composition. The effects of REEs and HMs on bacterial communities were similar, whereas their combined contributions were greater than the individual effects of REEs or HMs. Some bacterial taxa were worth noting. These specifically included the plant growth-promoting bacteria Exiguobacterium (sensitive to REEs and HMs) and oligotrophic microorganisms with metal tolerance (prevalent in contaminated soil); moreover, relative abundance of JTB255-Marine Benthic Group, Rhodobacteraceae, Erythrobacter, and Truepera may be correlated with REEs. This study was the first to investigate the responses of bacterial communities to REE and HM co-contamination. The current results have major implications for the ecological risk assessment of environments co-contaminated with REEs and HMs.

长期稀土元素 (REE) 和重金属 (HM) 污染对土壤细菌群落的影响仍然知之甚少。在这项研究中，从稀土尾矿坝收集了与 REE 和 HM 共污染的土壤样品。使用 16S rRNA 基因扩增子通过 Illumina 高通量测序分析细菌群落组成和多样性。共污染土壤的细菌群落丰富度和多样性低于未污染土壤，细菌群落组成明显不同。结果表明，总有机碳和速效钾是影响细菌群落丰富度和多样性的最重要因素，其次是REE和HM含量。虽然典型对应分析结果表明单独的REE对细菌群落结构没有明显影响，但我们发现土壤理化性质和REE和HM含量的共同作用调节了细菌群落结构和组成。REE 和 HMs 对细菌群落的影响相似，但它们的综合贡献大于 REE 或 HMs 的单个影响。一些细菌类群值得注意。这些特别包括植物生长促进细菌 而它们的综合贡献大于 REE 或 HM 的单个影响。一些细菌类群值得注意。这些特别包括植物生长促进细菌 而它们的综合贡献大于 REE 或 HM 的单个影响。一些细菌类群值得注意。这些特别包括植物生长促进细菌微小杆菌（对 REE 和HM敏感）和具有金属耐受性的寡营养微生物（在污染土壤中普遍存在）；此外，JTB255-海洋底栖生物组，Rhodobacteraceae，相对丰度赤，和Truepera可以与稀土元素相关。这项研究首次调查了细菌群落对 REE 和 HM 共污染的反应。目前的结果对稀土元素和重金属共污染环境的生态风险评估具有重要意义。