Etique M, Jorand F P A, Ruby C
Université de Lorraine, Laboratoire de Chimie Physique et Microbiologie pour l'Environnement, Villers-lès-Nancy, France.
CNRS, Laboratoire de Chimie Physique et Microbiologie pour l'Environnement, Villers-lès-Nancy, France.
Geobiology. 2016 May;14(3):237-54. doi: 10.1111/gbi.12170. Epub 2015 Dec 30.
Magnetite (Fe(II) Fe(III) 2 O4 ) is often considered as a stable end product of the bioreduction of Fe(III) minerals (e.g., ferrihydrite, lepidocrocite, hematite) or of the biological oxidation of Fe(II) compounds (e.g., siderite), with green rust (GR) as a mixed Fe(II) -Fe(III) hydroxide intermediate. Until now, the biotic transformation of magnetite to GR has not been evidenced. In this study, we investigated the capability of an iron-reducing bacterium, Shewanella putrefaciens, to reduce magnetite at circumneutral pH in the presence of dihydrogen as sole inorganic electron donor. During incubation, GR and/or siderite (Fe(II) CO3 ) formation occurred as secondary iron minerals, resulting from the precipitation of Fe(II) species produced via the bacterial reduction of Fe(III) species present in magnetite. Taking into account the exact nature of the secondary iron minerals and the electron donor source is necessary to understand the exergonic character of the biotic transformation of magnetite to GR, which had been considered to date as thermodynamically unfavorable at circumneutral pH. This finding reinforces the hypothesis that GR would be the cornerstone of the microbial transformations of iron-bearing minerals in the anoxic biogeochemical cycle of iron and opens up new possibilities for the interpretation of the evolution of Earth's history and for the understanding of biocorrosion processes in the field of applied science.
磁铁矿（Fe(II)Fe(III)₂O₄）通常被认为是Fe(III)矿物（如针铁矿、纤铁矿、赤铁矿）生物还原或Fe(II)化合物（如菱铁矿）生物氧化的稳定终产物，绿锈（GR）是一种混合的Fe(II)-Fe(III)氢氧化物中间体。到目前为止，尚未有证据证明磁铁矿向GR的生物转化。在本研究中，我们研究了一种铁还原细菌——腐败希瓦氏菌在以氢气作为唯一无机电子供体的情况下，在接近中性pH值条件下还原磁铁矿的能力。在培养过程中，作为次生铁矿物会形成GR和/或菱铁矿（Fe(II)CO₃），这是由于磁铁矿中存在的Fe(III)物种被细菌还原产生的Fe(II)物种沉淀所致。考虑次生铁矿物的确切性质和电子供体来源对于理解磁铁矿向GR生物转化的放能特性是必要的，迄今为止，这种转化在接近中性pH值时被认为在热力学上是不利的。这一发现强化了以下假设：GR是铁在缺氧生物地球化学循环中含铁矿石微生物转化的基石，并为解释地球历史演变以及理解应用科学领域中的生物腐蚀过程开辟了新的可能性。
