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

深层生物圈指的是位于大陆表面和海洋底部以下的任何栖息地，占地球总生物量的很大一部分。生物圈深处生活着种类繁多且大多没有特征的微生物，它们可能在调节全球生物地球化学过程中发挥作用。了解这一领域的起源、演化和意义对于阐明深层生物圈在地球生物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，这反过来又可能提供对太阳系其他地方生命的洞察。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30年的研究工作中受到了相当大的关注。尽管如此，它是地球上最鲜为人知的生态系统。国际海洋发现计划(IODP)提供了进入深层生物圈的途径。以往在蒙特塞拉特(340号考察队，U1396号考察队)和阿留申群岛(323次考察队，U1339号考察队)近海探险中发现的沉积物岩芯的特征是整个区段中存在的有机质。这些地点既包括背景沉积物，主要来自浮游生物遗骸通过水柱(U1396点富含碳酸盐，U1339点富含二氧化硅)的沉淀物，也包括火山成因产品。后一种来源之所以出现，是因为这两个地点都靠近火山，导致火山喷发的物质迅速输送到海洋中。一直以来，保存在火山物质(称为火山灰)中的有机物质与保存在背景沉积物中的有机物质有很大的不同。在Tephra中特别感兴趣的是一系列酰胺和磺胺化合物(具有-NH2官能团的化合物)，它们要么丰度低得多，要么在背景沉积物中完全不存在。这些化合物被假设为来自于苔藓内的微生物活动。在水和非洲菊接触的其他地方也发现了非洲菊的微生物定居现象，并建议由各种微生物合成类似的化合物。不幸的是，没有在U1339和U1396地点进行微生物学研究，因此这项研究的目的是在日本室户海岸的一个新地点进一步检验这一假说。该遗址以前曾被钻探过，并含有大量的非洲菊。IODP探险370的目标是在这一地区再次钻探，特别是调查深层生物圈内的微生物，使这里成为检验我们假设的理想地点和时间。这项研究可以解决几个问题：1)在温度和其他环境因素的范围内，沉积物中是否存在与微生物活性有关的独特的新有机化合物？2)这些化合物的浓度和组成是否随微生物活动的强度而变化？如果是这样的话，我们能用它们作为活性的替代测量吗？3)这些化合物的浓度和组成是否会随着沉积物/孔隙水的组成而变化？4)不再包含微生物活性的沉积物中是否存在生物标志物？如果是这样的话，我们能用它们作为过去微生物活动的生物标志物吗？探险370样品将首次得到深度/温度、微生物脂类和微生物群落组成的良好限制剖面。这提供了一个机会来检验我们的假设，并以一种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，我们也许能够利用这些化合物作为极端/古老环境中的生命示踪物，例如在已知经历过火山活动的地区(如火星)寻找整个太阳系的生命。

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).