CERBERUS Cataclastic hydrogen and oxidant production in the deep biosphere: uncovering the ancient role of microbial antioxidant enzymes

据估计，在我们脚下的深层岩石和沉积物中，有比地球表面或地球上更多的微生物生命——然而，我们对这些生命如何在没有光和光合作用的情况下生存的理解仍然存在很大的差距。现在有强有力的证据表明，水与岩石反应产生的氢气是地下微生物的重要能量（或食物）来源，这种氢气的使用可以追溯到地球上最早的生命出现。地下氢气的一个重要来源是沿着地质断层的岩石研磨产生的，新破裂的岩石表面“分裂”水形成氢气，同时还有等量的氧当量（氧化剂），如用于漂白的高氧化和有毒的化学物质过氧化氢。虽然以前的研究已经测量了地质断层产生的氢的数量，但CERBERUS关注的是方程式的另一边——氧化剂发生了什么？通过最初的实验，我们发现这些氧化剂很可能只有在非常热的温度下才会从矿物质中释放出来，在这种温度下，只有最喜欢热的微生物，即超嗜热微生物，才能在接近或超过水沸点的温度下生存和繁衍。从回溯所有生命共有的特定基因到最后的普遍共同祖先（LUCA）的研究中，我们知道，这种耐热微生物很可能是地球上最早出现的生命，而且它们使用氢。然而，基因回溯也表明LUCA含有丰富的处理氧气和过氧化氢的机制，而“普遍生命之树”中一些最根深蒂固的分支含有利用氧气的微生物。迄今为止，最被广泛接受的关于这些利用氧气的基因的原因是，它们是在地球上产生氧气的光合作用进化之后所有生命后来的基因“污染”的结果，在生命最初开始的数亿年之后。在CERBERUS中，我们建议另一种选择。生命最初出现在高温的地下裂缝中，那里不仅有氢，而且有水在破裂的岩石表面分解产生的过氧化氢。我们进一步认为，这些微生物进化出了对抗这些氧化剂的关键酶，包括那些可以将毒性更大的过氧化氢转化为毒性更小的氧气的酶，并在此过程中产生可用的能量，为生命提供动力并推动进一步的进化。CERBERUS将进行新的实验，测量氢气和氧化剂是如何在断裂的岩石-水反应中产生的，达到或超过已知的当前寿命极限（122摄氏度）。在一些实验中，我们会加入纯的超嗜热微生物菌株，看看它们如何改变反应的产物，看看它们是否能从反应中产生的氢、过氧化氢和氧中生长。“CERBERUS”的结果将揭示生命如何在地球深处、炎热的地下生存，并深入了解早期生命是如何在我们的星球上扎根的。

CERBERUS - SummaryIt has been estimated that there is more microbial life under our feet in deep rocks and sediments than there is on the surface or our planet - yet there are still large gaps in our understanding of how this life survives in the absence of light and photosynthesis. There is now strong evidence that hydrogen gas, produced by water reacting with rocks, is an important source of energy (or food) for subsurface microbes - and that the use of this hydrogen dates back to the very first life that arose on Earth. A very substantial source of subsurface hydrogen is generated from the grinding of rocks along geological faults, with freshly fractured rock surfaces 'splitting' water to form hydrogen gas, alongside an equal amount of oxygen equivalent (oxidants) such as the highly oxidizing and toxic chemical hydrogen peroxide, used in bleaching.While previous studies have measured the amount of hydrogen produced during geological faulting, CERBERUS focuses on the other side of the equation - what happens to the oxidants? Through initial experiments we show that these oxidants are likely only being released from minerals at very hot temperatures where only the most heat-loving microorganisms, known as hyperthermophiles, can live and thrive, at temperatures close to or over the boiling point of water. From studies back-tracing particular genes common to all life to a Last Universal Common Ancestor (LUCA) we know that such heat-living microorganisms were likely to have been the first life to arise on Earth, and that they used hydrogen. However, the gene back-tracing has also suggested that LUCA contained abundant mechanisms for dealing with oxygen and hydrogen peroxide, while some of the most deeply rooted braches of the 'universal tree of life' contain oxygen utilizing microorganisms. To date, the most widely accepted reason for these oxygen-utilizing genes is that they result from later genetic 'contamination' of all life after the oxygen-producing photosynthesis evolved on our planet, many hundreds of millions of years after life first started. In CERBERUS, we suggest an alternative. That life first arose in hot, subsurface fractures where there was not only hydrogen present, but also hydrogen peroxide produced from water splitting on fractured rock surfaces. We further suggest that these microorganisms evolved key enzymes to combat these oxidants, including those that could convert the more toxic hydrogen peroxide to less toxic oxygen - and in doing so generate usable energy to power life and drive further evolution.CERBERUS will carry out new experiments, measuring how both hydrogen and oxidants are produced in fractured rock-water reactions up to and beyond the known limit of current life (122 deg C). To some experiments we will add pure strains of hyperthermophilic microorganisms, to see how they can alter the products of the reactions, and to see if they can grow from the hydrogen, hydrogen peroxide and oxygen produced during the reactions. Results from CERBERUS should shine a light on how life can survive in the Earth's deep, hot subsurface - and give insight into how early life took hold on our planet.