Metalliferous Biosignatures for Deep Subsurface Microbial Activity.
Metalliferous Biosignatures for Deep Subsurface Microbial Activity.
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DOI：
10.1007/s11084-015-9466-x
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发表时间：
2016-03
期刊：
影响因子：
--
通讯作者：
Bowden S
中科院分区：
文献类型：
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作者：
Parnell J;Brolly C;Spinks S;Bowden S
人们普遍认为微生物和金属的相互作用发生在地表或非常浅的地下环境中。然而，新的证据表明，许多微生物活动发生在地下深处。河流、湖泊和风成的“红层”中含有广泛分布的厘米级还原球体，其中红色岩石中的浅色还原球体含有含金属核。沉积物中Fe（III）的还原主要是由Fe（III）还原菌引起的。它们具有还原一系列金属和准金属的潜力，包括V、Cu、Mo、U和Se，通过将它们取代Fe（III）作为电子受体，这些元素都是还原球体中常见的元素。球状形态表明，它们是在压实后在深度处形成的，这与微生物形成一致。鉴于Fe（III）还原的后果具有视觉表达，它们是陆地和地外地质记录勘探期间的潜在生物特征。关于火星上Fe（III）还原所提供的能量存在争议，但火星土壤中丰富的铁使其成为最有价值的生命前景之一。微生物本身作为化石被捕获是可能的，但在火星探索过程中更现实的目标是反映选择性还原或氧化的颜色对比。这可以通过使用拉曼光谱法分析还原球体上的石英颗粒来实现，这证明了其适用于地下环境中的生命检测。微生物作用是形成还原球状体的最合适的解释，并可能作为深部地下微生物活动的含金属生物标志。
The interaction of microbes and metals is widely assumed to have occurred in surface or very shallow subsurface environments. However new evidence suggests that much microbial activity occurs in the deep subsurface. Fluvial, lacustrine and aeolian ‘red beds’ contain widespread centimetre-scale reduction spheroids in which a pale reduced spheroid in otherwise red rocks contains a metalliferous core. Most of the reduction of Fe (III) in sediments is caused by Fe (III) reducing bacteria. They have the potential to reduce a range of metals and metalloids, including V, Cu, Mo, U and Se, by substituting them for Fe (III) as electron acceptors, which are all elements common in reduction spheroids. The spheroidal morphology indicates that they were formed at depth, after compaction, which is consistent with a microbial formation. Given that the consequences of Fe (III) reduction have a visual expression, they are potential biosignatures during exploration of the terrestrial and extraterrestrial geological record. There is debate about the energy available from Fe (III) reduction on Mars, but the abundance of iron in Martian soils makes it one of the most valuable prospects for life there. Entrapment of the microbes themselves as fossils is possible, but a more realistic target during the exploration of Mars would be the colour contrasts reflecting selective reduction or oxidation. This can be achieved by analysing quartz grains across a reduction spheroid using Raman spectroscopy, which demonstrates its suitability for life detection in subsurface environments. Microbial action is the most suitable explanation for the formation of reduction spheroids and may act as metalliferous biosignatures for deep subsurface microbial activity.