Exploring microbial sulphate reduction under high temperature and pressure

即使在几公里深的沉积层中也有活跃的微生物。温度随着深度的增加而增加，最终超过了生命可能存在的极限。到目前为止，发现寿命的上限约为120° C。它是在热液系统的微生物中发现的，即所谓的黑烟。然而，在沉积物中，温度上限似乎要低得多。来自油田的数据表明，极限温度约为80° C。热液系统和沉积系统之间的差异是由于微生物在沉积系统中无法获得足够的能量来在更高的温度下进行蛋白质和DNA等生物分子的修复。有趣的是，只有在高压下进行实验时，才有可能证明实验室中非常高温下的代谢活动。IODP Expedition 370是专门为解决沉积系统中生命的温度上限问题而设计的。在日本近海的南海海槽，地热梯度约为100° C/km，这意味着生命的整个温度范围延伸到略多于一公里的深度间隔。通过使用最先进的钻探和实验室技术，有可能获得绝对原始的样品，没有任何污染。这次考察具有高度的跨学科性质，因此测量了大量的生物和化学参数，从而能够对沉积物进行非常详细的描述。拟议项目是考察的一个重要组成部分，因为硫酸盐还原是海底有机物降解的最重要的厌氧过程。在硕士论文的框架内，已经进行了硫酸盐还原速率的首次测量，并且他们证明了这一过程确实发生在整个取芯深度区间，尽管速率非常低。作为拟议项目的一部分，计划在高压条件下进行更多的测量。为了实现这一点，应建造和运行高压热梯度系统。除了南开海槽的沉积物外，我们还计划用瓜伊马斯盆地的热液影响物质进行实验。将这些沉积物与沉积物类型进行比较，将有助于更深入地了解海底最重要的生物过程之一的运作以及一般生命的局限性。

Even in deep sediment layers under several kilometers of sediments there are active microorganisms. Temperature increases with depth and eventually exceeds the limit to which life is possible. So far the upper limit of life was found to be around 120° C. It was found in microorganisms from hydrothermal systems, the so-called Black Smokers. In sediments however the upper temperature limit appears to be much lower. Data from oilfields indicate a limit around 80° C. The discrepancy between hydrothermal and sedimentary systems was explained by the fact that microorganisms cannot gain enough energy in sedimentary systems to carry out the repair of their biomolecules like proteins and DNA at higher temperatures. Interestingly, the proof of metabolic activity at very high temperatures in the lab is only possible when the experiments are carried out at high pressure. IODP Expedition 370 was specifically designed to solve the question of the upper temperature limit of life in sedimentary systems. In the Nankai Trough off the coast of Japan the geothermal gradient is around 100° C/km, which means that the entire temperature range of life stretches over a depth interval of slightly more than one kilometre. By using the most advanced drilling and laboratory techniques it was possible to obtain absolutely pristine samples that are devoid of any contamination. The expedition had a highly interdisciplinary character so that a multitude of biological and chemical parameter was measured, allowing a very detailed characterization of the sediment. The proposed project is an important component of the expedition because sulphate reduction is the quantitatively most important anaerobic process for degradation of organic matter in the seabed. Within the framework of an MSc thesis first measurements of sulphate reduction rates were already carried out and they proved that this process does indeed occur over the entire cored depth interval, albeit at very low rates. As part of the proposed project more measurements are planned, also under high pressure conditions. In order to achieve this a high pressure thermal gradient system shall be constructed and operated. Additional to sediments from Nankai Trough we plan for experiments with hydrothermally influenced material from Guaymas Basin. Comparison between these to types of sediment will allow deeper understanding of the functioning of one of the most important biological processes in the sea floor and the limits of life in general.