Hydrogen Generation in the Deep, Hot Biosphere

1995年在玄武岩地层中发现了地下自养微生物生态系统(黏液)，似乎利用了水-岩相互作用形成的氢，因为这个厌氧群落可以独立于表面光合作用，包括有机物和氧气。这种潜在的大量能源供应也可能解释为什么在地下陆地环境(至少到3公里深)中发现了令人惊讶的大量原核生物，尽管条件极端，缺乏明显的能源供应。它还具有深远的天体生物学意义，因为它是行星上亚表面生命的一种机制，即使表面条件不适合生命也是如此。然而，这种氢气产生的意义是有争议的，因为它被批评为在环境中可以忽略不计的反应(条件太碱性，受到矿物中有限的还原铁浓度的限制，以及它对新反应表面产生的依赖)。然而，在地震断裂带的深处也检测到了氢气的形成，有间接证据表明，地下原核生物利用氢气来产生甲烷。这种情况下氢的形成机制被认为是由于地震区岩石的地下破裂引起的机械力化学作用。如果这是真的，那么在每年超过20000次以上的地震中，任何类型的岩石都有可能产生氢气，这使得形成大量黏液群落的可能性明显增加。此外，我们已经证明，一些原核生物实际上可能加速从沉积物浆液中的矿物生成氢气，包括从纯硅砂中生成氢气。由于硅酸盐约占地壳的95%，这可能是氢气的重要来源。我们打算通过测试一系列常见的矿物和产氢条件，包括在升高温度的情况下模拟由于沉积物埋藏而发生的加热，来进一步研究这些氢气形成的机制。我们将确定微生物过程是否受到产氢的刺激，并鉴定和培养涉及的微生物。然后，这些浓缩的微生物将与纯矿物质一起使用，以更详细地研究它们参与并将矿物质用作能源的能力。一些高压实验将使温度高达150摄氏度的研究成为可能。对于微生物(max~120oC)来说，这太高了，但可能会产生氢和其他化合物，这些化合物可以向上扩散，以喂养生物圈的底部。还将进行新的密封岩石粉碎实验(30-120oC)，以测试仅岩石破裂是否就能产生足够的氢气来养活微生物种群。

The discovery of the Subsurface LithoAutotrophic Microbial Ecosystem (SLiME) in basalt formations in 1995, seemingly using hydrogen formed from water rock interactions, was of great significance as this anaerobic community could be independent of surface photosynthesis, both organic matter and oxygen. This potentially significant energy supply might also explain the surprisingly large numbers of prokaryotes found in subsurface terrestrial environment (at least to 3 km depth), despite extreme conditions and lack of obvious energy supply. It also has profound astrobiological significance as a mechanism for subsurface life in planets even with surface conditions that are unsuitable for life. However, the significance of this hydrogen generation is controversial having being criticized as being a negligible reaction in the environment (conditions too alkaline, restricted by limited reduced iron concentrations in minerals and by its dependence on the production of fresh reactive surfaces). However, hydrogen formation has also been detected at depth in earthquake fault zones and there is indirect evidence that this is used by subsurface prokaryotes to produce methane. The mechanism of hydrogen formation in this case is thought to be due to mechanochemistry as a result of subsurface fracturing of rocks in earthquake zones. If this is true then with some greater than 20,000 earthquakes a year any rock type could potentially produce hydrogen making a substantial SLiME community distinctly more possible. In addition, we have demonstrated that some prokaryotes may actually speed-up hydrogen formation from minerals in sediment slurries, including hydrogen generation from pure silica sand. As silicates make up ~95% of the Earth's crust this could potentially be a significant source of hydrogen. We intend to investigate further these mechanisms of hydrogen formation by testing a range of common minerals and conditions for hydrogen generation, including at increasing temperatures to simulate the heating that occurs due to sediment burial. We will determine whether microbial processes are stimulated by hydrogen formation and identify and culture the microbes involved. These enriched microbes will then be used with pure minerals to investigate their involvement and ability to use the mineral as an energy source in more detail. Some high pressure experiments will enable temperatures up to 150oC to be investigated. This is too high for microbes (max ~120oC) but may produce hydrogen and other compounds which can diffuse upwards to feed the base of the biosphere. Novel sealed rock crushing experiments will also be conducted (30 - 120oC) to test whether just cracking of rocks can produce enough hydrogen to feed a microbial population.