The reduction of hexavalent chromium [Cr(VI)] by microbiota agents is a potential method for ecological remediation in heavily contaminated soil. This study investigated the contribution of microbial community and extracellular polymeric substances (EPS) to reduce Cr(VI) using lab-cultured anaerobic granular sludge (AGS). The AGS demonstrated an impressive reduction efficiency of 99.3% for Cr(VI) in soil, operating within an initial Cr(VI) concentration range of 500–3000 mg/kg. The distribution of typical electron acceptors, e.g., SO, NO, and Fe, had a negligible influence on microbial Cr(VI) reduction. The contribution of EPS on Cr(VI) reduction accounted for only 2.1% of the total Cr(VI) reduction, implying that Cr(VI) reduction driven by AGS was primarily caused by the direct effect of microbiota. High-throughput sequencing analysis confirmed that an increasing trend in the relative abundance of Cr reduction bacteria (: 0.40–5.54%, : 0.41–5.70%, : 0.35–6.64%, etc.), and the stability (0.716–4.114) of microbial co-occurrence networks was significantly promoted by the end of the experiment. Materials characterization indicated that successful reduction of Cr(VI) to trivalent chromium [Cr(III)] and formed in Cr(OH), and functional groups, O-H, N-H, -CH, and -CH, of AGS likely played a vital role in Cr(VI) reduction. Overall, these findings offer insights into the remediation technique of microbial Cr(VI) reduction in highly-contaminated soil based on the interaction network stability of the microbial community in AGS.

中文翻译：

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在厌氧颗粒污泥还原六价铬方面，微生物群落优于细胞外聚合物

通过微生物菌剂还原六价铬[Cr(VI)]是严重污染土壤生态修复的一种潜在方法。本研究利用实验室培养的厌氧颗粒污泥 (AGS) 调查了微生物群落和细胞外聚合物 (EPS) 对减少 Cr(VI) 的贡献。 AGS 在 500–3000 mg/kg 的初始 Cr(VI) 浓度范围内运行，对土壤中的 Cr(VI) 具有高达 99.3% 的令人印象深刻的还原效率。典型电子受体（例如SO、NO 和Fe）的分布对微生物Cr(VI) 还原的影响可以忽略不计。 EPS对Cr(VI)还原的贡献仅占Cr(VI)还原总量的2.1%，这意味着AGS驱动的Cr(VI)还原主要是由微生物群的直接作用引起的。高通量测序分析证实，Cr还原菌的相对丰度呈增加趋势（：0.40-5.54%、：0.41-5.70%、：0.35-6.64%等），稳定性（0.716-4.114）。实验结束时，微生物共现网络得到显着促进。材料表征表明，Cr(VI) 成功还原为三价铬 [Cr(III)] 并形成 Cr(OH)，AGS 的官能团 OH、NH、-CH 和 -CH 可能发挥了至关重要的作用Cr(VI) 还原。总体而言，这些发现为基于 AGS 中微生物群落相互作用网络稳定性的重度污染土壤中微生物 Cr(VI) 还原修复技术提供了见解。