Promotion of Humic Acid Transformation by Abiotic and Biotic Fe Redox Cycling in Nontronite,Environmental Science & Technology

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Promotion of Humic Acid Transformation by Abiotic and Biotic Fe Redox Cycling in Nontronite
Environmental Science & Technology ( IF 10.8 ) Pub Date : 2023-11-16 , DOI: 10.1021/acs.est.3c05646
Dafu Hu _{1,

2} , Qiang Zeng _{1,

2,

3} , Jin Zhu ₄ , Chen He ₅ , Quan Shi ₅ , Hailiang Dong _{1,

2,

3}

Affiliation

The redox activity of Fe-bearing minerals is coupled with the transformation of organic matter (OM) in redox dynamic environments, but the underlying mechanism remains unclear. In this work, a Fe redox cycling experiment of nontronite (NAu-2), an Fe-rich smectite, was performed via combined abiotic and biotic methods, and the accompanying transformation of humic acid (HA) as a representative OM was investigated. Chemical reduction and subsequent abiotic reoxidation of NAu-2 produced abundant hydroxyl radicals (thereafter termed as ·OH) that effectively transformed the chemical and molecular composition of HA. More importantly, transformed HA served as a more premium electron donor/carbon source to couple with subsequent biological reduction of Fe(III) in reoxidized NAu-2 by Geobacter sulfurreducens, a model Fe-reducing bacterium. Destruction of aromatic structures and formation of carboxylates were mechanisms responsible for transforming HA into an energetically more bioavailable substrate. Relative to unaltered HA, transformed HA increased the extent of the bioreduction by 105%, and Fe(III) reduction was coupled with oxidation and even mineralization of transformed HA, resulting in bleached HA and formation of microbial products and cell debris. ·OH transformation slightly decreased the electron shuttling capacity of HA in bioreduction. Our results provide a mechanistic explanation for rapid OM mineralization driven by Fe redox cycling in redox-fluctuating environments.

中文翻译：

绿脱石中非生物和生物铁氧化还原循环促进腐植酸转化

含铁矿物的氧化还原活性与氧化还原动态环境中有机物（OM）的转化有关，但其潜在机制仍不清楚。在这项工作中，通过非生物和生物相结合的方法对绿脱石（NAu-2）（一种富含铁的蒙皂石）进行了铁氧化还原循环实验，并研究了作为代表性有机物质的腐殖酸（HA）的伴随转化。 Nau-2 的化学还原和随后的非生物再氧化产生了丰富的羟基自由基（以下称为·OH），有效地改变了 HA 的化学和分子组成。更重要的是，转化的HA作为更优质的电子供体/碳源，与随后由硫还原地杆菌（一种模型铁还原细菌）对再氧化的NAu-2中的Fe(III)进行生物还原相结合。芳香族结构的破坏和羧酸盐的形成是将HA转化为能量上更具生物利用度的底物的机制。相对于未改变的HA，转化的HA将生物还原程度提高了105%，并且Fe(III)的还原与转化的HA的氧化甚至矿化相结合，导致HA漂白并形成微生物产物和细胞碎片。 ·OH转化略微降低了HA在生物还原中的电子穿梭能力。我们的研究结果为氧化还原波动环境中 Fe 氧化还原循环驱动的快速 OM 矿化提供了机制解释。

更新日期：2023-11-16

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