Biogeomagnetism Group, Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China.
Geomicrobiology, Center for Applied Geosciences, University of Tuebingen, Tuebingen 72074, Germany.
Environ Sci Technol. 2020 Apr 7;54(7):4121-4130. doi: 10.1021/acs.est.9b07095. Epub 2020 Mar 17.
Magnetite (FeO) is an environmentally ubiquitous mixed-valent iron (Fe) mineral, which can form via biotic or abiotic transformation of Fe(III) (oxyhydr)oxides such as ferrihydrite (Fh). It is currently unclear whether environmentally relevant biogenic Fh from Fe(II)-oxidizing bacteria, containing cell-derived organic matter, can transform to magnetite. We compared abiotic and biotic transformation: (1) abiogenic Fh (aFh); (2) abiogenic Fh coprecipitated with humic acids (aFh-HA); (3) biogenic Fh produced by phototrophic Fe(II)-oxidizer SW2 (bFh); and (4) biogenic Fh treated with bleach to remove biogenic organic matter (bFh-bleach). Abiotic or biotic transformation of Fh was promoted by Fe or Fe(III)-reducing bacteria. Fe-catalyzed abiotic reaction with aFh and bFh-bleach led to complete transformation to magnetite. In contrast, aFh-HA only partially (68%) transformed to magnetite, and bFh (17%) transformed to goethite. We hypothesize that microbial biomass stabilized bFh against reaction with Fe. All four Fh substrates were transformed into magnetite during biotic reduction, suggesting that Fh remains bioavailable even when associated with microbial biomass. Additionally, there were poorly ordered magnetic components detected in the biogenic end products for aFh and aFh-HA. Nevertheless, abiotic transformation was much faster than biotic transformation, implying that initial Fe concentration, passivation of Fh, and/or sequestration of Fe(II) by bacterial cells and associated biomass play major roles in the rate of magnetite formation from Fh. These results improve our understanding of factors influencing secondary mineralization of Fh in the environment.
磁铁矿（FeO）是一种在环境中普遍存在的混合价态铁（Fe）矿物，可以通过生物或非生物转化铁（III）（氧）氢氧化物（如纤铁矿（Fh））形成。目前尚不清楚是否含有细胞衍生有机质的源自亚铁氧化细菌的环境相关生物成因 Fh 可以转化为磁铁矿。我们比较了非生物和生物转化：（1）非生物成因 Fh（aFh）；（2）与腐殖酸共沉淀的非生物成因 Fh（aFh-HA）；（3）由光养亚铁氧化菌 SW2 产生的生物成因 Fh（bFh）；和（4）用漂白剂处理以去除生物有机质的生物成因 Fh（bFh-bleach）。Fh 的非生物或生物转化受 Fe 或 Fe（III）还原菌的促进。aFh 和 bFh-bleach 的 Fe 催化非生物反应导致完全转化为磁铁矿。相比之下，aFh-HA 仅部分（68％）转化为磁铁矿，而 bFh（17％）转化为针铁矿。我们假设微生物生物量稳定了 bFh 以防止与 Fe 反应。在生物还原过程中，所有四种 Fh 底物均转化为磁铁矿，这表明即使与微生物生物量相关联，Fh 仍具有生物可利用性。此外，在 aFh 和 aFh-HA 的生物成因最终产物中还检测到了无序的磁性成分。尽管如此，非生物转化的速度还是比生物转化快得多，这意味着初始 Fe 浓度，Fh 的钝化以及/或细菌细胞和相关生物量对 Fe(II)的螯合在 Fh 形成磁铁矿的速度中起主要作用。这些结果提高了我们对影响环境中 Fh 次生矿化的因素的理解。
