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更多的微生物生命，而不是在地表或我们的星球上-然而，我们对这种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来源（或食物）-并且这种氢气的使用可以追溯到地球上出现的第一个生命。地下氢的一个非常重要的来源是由岩石沿着地质断层的研磨产生的，新鲜破碎的岩石表面“分裂”水形成氢气，同时产生等量的氧当量（氧化剂）如用于漂白的高氧化性和毒性化学品过氧化氢。虽然以前的研究测量了地质断层作用产生的氢的数量，CERBERUS专注于等式的另一边-氧化剂会发生什么？通过最初的实验，我们表明这些氧化剂可能只在非常热的温度下从矿物质中释放出来，只有最喜欢热的微生物（称为超嗜热菌）才能在接近或超过水沸点的温度下生存和茁壮成长。通过追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，我们知道这种热生活微生物可能是地球上出现的第一个生命，并且它们使用氢。然而，基因回溯也表明，LUCA含有丰富的机制，处理氧气和过氧化氢，而一些最根深蒂固的分支的"生命之树“含有利用氧气的微生物。到目前为止，这些利用氧气的基因最广泛接受的原因是，它们是在我们星球上进化出产生氧气的光合作用之后，在生命开始之后数亿年，所有生命的遗传“污染”的结果。在地狱犬中，我们提出了另一种选择。这种生命最初出现在炎热的地下裂缝中，那里不仅有氢，而且还有水在裂缝岩石表面分裂产生的过氧化氢。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，推动进一步进化。测量氢和氧化剂是如何在断裂的岩石-水反应中产生的，直到和超过目前已知的寿命极限（122摄氏度）。在某些实验中，我们将加入纯的极端嗜热微生物菌株，看看它们如何改变反应产物，看看它们是否能从反应过程中产生的氢、过氧化氢和氧中生长。CERBERUS的研究结果应该能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如何在我们的星球上扎根。

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.