Assessing the utility of trace and rare earth elements as biosignatures in microbial iron oxyhydroxides
Assessing the utility of trace and rare earth elements as biosignatures in microbial iron oxyhydroxides
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DOI：
10.3389/feart.2015.00006
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发表时间：
2015-01-01
影响因子：
2.9
通讯作者：
Thiel, Volker
中科院分区：
文献类型：
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作者：
Heim, Christine;Simon, Klaus;Thiel, Volker
微生物氧化铁是天然水体、近期沉积物和矿井排水系统中常见的沉积物。与这些矿物一起，微量和稀土元素（TREE）正在矿化微生物席中积累。TREE模式被广泛用于描述矿物和岩石的特征，并阐明它们的演化和起源。然而，是否以及哪些特征TREE特征区分铁矿物的生物和非生物起源仍然不清楚。在这里，我们报告了在阿斯波隧道（阿斯波硬岩实验室，瑞典）进行的长期流动反应器研究。研究了以铁氧化菌（FeOB） mariproundus sp.和Gallionella sp.为主的微生物席的发育情况。流动反应器的喂料流体在海平面以下183米和290米的地方从周围两个咸淡水含水层中提取，但化学成分不同，类似于1.8 Ga的花岗闪长岩。实验研究了地下大陆生物圈受控条件下TREE的积累和分馏，并使我们能够评估微生物铁氢氧化物中潜在的生物特征演变。2个月和9个月后，微生物垫中Be、Y、Zn、Zr、Hf、W、Th、Pb和U的浓度分别比喂料液高10(3)~ 10(5)倍，稀土元素和Y （REE+Y）含量分别高10(4)~ 10(6)倍。除热液引起的Eu异常外，微生物铁氧氢氧化物的归一化REE+Y模式与已发表的太古宙带状铁组（BIFs）的REE+Y分布非常相似。将流动反应器中的微生物氧化铁与从同一进料液中人工沉淀的氧化铁进行了比较。值得注意的是，这些非生物和无机铁氢氧化物具有相同的REE+Y分布模式。我们的研究结果表明，REE+Y密切反映了水的化学性质，但它们不能区分微生物介导的铁沉淀和无机铁沉淀。同样，所有的TREE研究都显示出在生物源、非生物和无机铁氢氧化物中总体上相似的分馏行为。例外的是Ni和TI，它们只在微生物铁氢氧化物中积累，可能表明这些元素作为微生物生物特征的潜在效用。
Microbial iron oxyhydroxides are common deposits in natural waters, recent sediments, and mine drainage systems. Along with these minerals, trace and rare earth elements (TREE) are being accumulated within the mineralizing microbial mats. TREE patterns are widely used to characterize minerals and rocks, and to elucidate their evolution and origin. However, whether and which characteristic TREE signatures distinguish between a biological and an abiological origin of iron minerals is still not wellunderstood. Here we report on long-term flow reactor studies performed in the Tunnel of Aspo (Aspo Hard Rock Laboratory, Sweden). The development of microbial mats dominated by iron-oxidizing bacteria (FeOB), namely Mariprofundus sp. and Gallionella sp were investigated. The feeder fluids of the flow reactors were tapped at 183 and 290 m below sealevel from two brackish, but chemically different aquifers within the surrounding, similar to 1.8 Ga old, granodioritic rocks. The experiments investigated the accumulation and fractionation of TREE under controlled conditions of the subsurface continental biosphere, and enabled us to assess potential biosignatures evolving within the microbial iron oxyhydroxides. After 2 and 9 months, concentrations of Be, Y, Zn, Zr, Hf, W, Th, Pb, and U in the microbial mats were 10(3)- to 10(5-)fold higher than in the feeder fluids whereas the rare earth elements and Y (REE+Y) contents were 10(4)- and 10(6)-fold enriched. Except for a hydrothermally induced Eu anomaly, the normalized REE+Y patterns of the microbial iron oxyhydroxides were very similar to published REE+Y distributions of Archaean Banded Iron Formations (BIFs). The microbial iron oxyhydroxides from the flow reactors were compared to iron oxyhydroxides that were artificially precipitated from the same feeder fluid. Remarkably, these abiotic and inorganic iron oxyhydroxides show the same REE+Y distribution patterns. Our results indicate that the REE+Y mirror closely the water chemistry, but they do not allow to distinguish microbially mediated from inorganic iron precipitates. Likewise, all TREE studied showed an overall similar fractionation behavior in biogenic, abiotic, and inorganic iron oxyhydroxides. Exceptions are Ni and TI, which were only accumulated in the microbial iron oxyhydroxides and may point to a potential utility of these elements as microbial biosignatures.