Novel organic compounds in tephra as indicators of current and past microbial activity

深层生物圈描述了位于大陆表面和海洋底部以下的任何栖息地，包括地球总生物量的大部分。多样且大多数未被表征的微生物生活在深层生物圈中，可能在调解全球生物地球化学过程中发挥作用。了解这一领域的起源，演变和意义对于阐明深层生物圈在地球地球化学中的作用以及了解微生物如何在这种极端环境中茁壮成长至关重要，这反过来又可能为了解太阳系其他地方的生命提供帮助。由于深层生物圈在地球上以及在寻找地外生命方面可能发挥的未知重要性，这一领域在过去三十年的研究工作中受到了相当大的关注。尽管如此，它仍然是地球上最不为人所知的生态系统。国际海洋发现计划（IODP）提供了进入深层生物圈的途径。从蒙特塞拉特海岸（远征340，网站U1396）和阿留申群岛（远征323，网站U1339）以前的探险回收的沉积物芯的特点是在整个部分存在的有机物。这些地点包括背景沉积物和火山产物，背景沉积物主要来自浮游生物遗骸通过水柱的沉降（地点U1396的碳酸盐含量高，地点U1339的二氧化硅含量高）。后一种来源的出现是因为这两个地点都靠近火山，导致火山爆发的物质迅速被输送到海洋。因此，火山物质中保存的有机物质（称为火山灰）与背景沉积物中保存的有机物质有很大不同。火山灰中特别令人感兴趣的是一系列酰胺和磺酰胺化合物（具有官能团-NH 2的化合物），这些化合物在背景沉积物中的丰度要低得多，或者完全不存在。这些化合物已被假设为源自火山灰内发生的微生物活动。在水和火山灰接触的其他地方也发现了火山灰的微生物定居，并且已经提出了由各种微生物合成类似的化合物。不幸的是，在研究中心U1339和U1396未进行微生物学研究，因此本研究的目的是在日本Muroto海岸外的新研究中心进一步检验这一假设。这个地方以前曾被钻探过，含有大量的火山灰。IODP Expedition 370旨在再次在该地区钻探，特别是调查深层生物圈中的微生物，使其成为测试我们假设的理想地点和时间。本研究可以解决以下几个问题：1）在沉积物中是否存在与温度和其他环境因素范围内的微生物活性相关的独特的新型有机化合物？2)这些化合物的浓度和组成是否根据微生物活性的强度而变化？如果是的话，我们可以用它们作为活动的替代指标吗？3)这些化合物的浓度和组成是否因沉积物/孔隙水组成而异？4)生物标志物在不再含有微生物活性的沉积物中是否持续存在？如果是的话，我们可以把它们作为过去微生物活动的生物标志物吗？远征370样品将首次具有深度/温度、微生物脂质和微生物群落组成的良好约束概况。这提供了一个机会来测试我们的假设，并以强有力的方式回答所概述的问题，并可能提供一套新的生物标志物，用于在极端环境中寻找生命。因此，我们可能能够使用这些化合物作为极端/古老环境中生命的示踪剂，例如在整个太阳系中已知经历过火山活动的地区（例如火星）寻找生命。

The deep biosphere describes any habitat located below the surface of the continents and the bottom of the ocean, and comprises much of Earth's total living biomass. Diverse and mostly uncharacterised microorganisms live in the deep biosphere, potentially playing a role in mediating global biogeochemical processes. Understanding the origin, evolution and significance of this realm is of fundamental importance for elucidating the role of the deep biosphere in Earth's biogeochemistry and understanding how microorganisms thrive in such extreme environments, which in turn may provide insight into life elsewhere in the solar system. Due to the unknown importance the deep biosphere may play on Earth and also in the search for extra-terrestrial life, this realm has received considerable attention in research endeavours over the past three decades. Despite this, it is the most poorly understood ecosystem on Earth.The International Ocean Discovery Program (IODP) provides access to the deep biosphere. Sediment cores recovered from previous expeditions off the coast of Montserrat (Expedition 340, Site U1396) and the Aleutian Islands (Expedition 323, Site U1339) have been characterised in terms of the organic matter present throughout the sections. These sites comprise both background sediments largely derived from settling of the remains of plankton through the water column (high in carbonate at Site U1396 and silica at U1339) and volcanogenic products. The latter source arises because both sites are proximal to volcanoes, resulting in material from erupted volcanoes being rapidly transported to the oceans. Consistently, the organic material preserved in the volcanic material (termed tephra) is very different from that preserved in the background sediments. Of particular interest within the tephra are a series of amide and sulphonamide compounds (compounds with the functional group -NH2) that are either in much lower abundance or completely absent in the background sediments. These compounds have been hypothesised to originate from microbial activity occurring within the tephra. Microbial colonisation of tephra has been found at other locations where water and tephra are in contact and similar compounds have been suggested to be synthesised by various microorganisms. Unfortunately, no microbiology studies were conducted at Sites U1339 and U1396, hence the aim of this study is to further test this hypothesis at a new site off the coast of Muroto, Japan. This site has been drilled before and contains significant volumes of tephra. IODP Expedition 370 aims to drill in this region again, specifically to investigate microorganisms within the deep biosphere, making this an ideal location and time to test our hypothesis. Several questions can be addressed with this research:1) Are there distinct novel organic compounds associated with microbiological activity over the range of temperature and other environmental factors in the sediments?2) Does the concentration and composition of these compounds vary according to the intensity of microbial activity? If so, can we use them as a proxy measure of activity?3) Does the concentration and composition of these compounds vary according to the sediment/porewater composition? 4) Do biomarkers persist in sediments that no longer contain microbial activity? If so, can we use them as biomarkers of past microbial activity?Expedition 370 samples will, for the first time, have well constrained profiles of depth/temperature, microbial lipids and microbial community composition. This presents the opportunity to test our hypothesis and answer the questions outlined in a robust manner, and potentially provide a new suite of biomarkers with which to look for life in extreme environments. Thus, we may be able to use these compounds as tracers of life in extreme/ancient environments such as in the search for life throughout the solar system in areas known to have experienced volcanism (e.g. Mars).