Molecular-life signatures and organic-matter transformations at the temperature limit of life, IODP Exp. 370

实验370的目的是探索日本南开海槽室东角附近深层生物圈的生命上限温度，该地点的热流非常高，沉积物-基底界面的温度预计将达到目前已知的生命温度极限，约为120摄氏度。这些温度也是发生后生作用的温度，即有机物质向液体和气态碳氢化合物的热分解。通过连锁反应，人们认为生物可利用的有机物质越不稳定，可能被氧化的越多，这就被提议在高温下直接喂养土著微生物群落，在这些非生物区和生物区之间提供联系。这个项目的首要研究问题是：深层生物圈接近生命温度极限的程度有多大？在能源有限的栖息地，生命是如何适应高温的？在有机碳含量较低的沉积物中，干酪根释放出哪些生物可利用的化合物？为接近生命温度极限的海底微生物系统提供燃料的底物是什么？这项提议打算实施一种全面的地球化学方法，其中将包括利用超灵敏质谱学技术对分子生命检测标记物，如完整的极性脂类和呼吸对苯二酚进行定量和定性的核心分析。这些研究将与可溶和不溶有机物质(干酪根)的详细特征密切相关。使用元素、质谱学、光谱和热解技术，将评估与干酪根结合的有机质的质量和生物可利用性。此外，将通过水合热解实验室实验来测试可能滋养本地微生物群落的有机底物生成的潜力。这项研究与当前深层生物圈研究的基本问题直接相关，并有望极大地促进我们对深层地下生物圈的范围以及可能最终限制深埋生命的因素的理解。

Exp. 370 was implemented to explore the upper temperature of life of the deep biosphere off Cape Muroto, Nankai Trough, Japan, a site with an extraordinarily high heat flow and where temperatures at the sediment-basement interface are expected to reach the currently known temperature limit of life at around 120°C. These are also temperatures where catagenesis, the thermal breakdown of organic material to liquid and gaseous hydrocarbons, occurs. Through the catagenic reactions it is assumed that the more labile and potentially more oxidized organic material becomes bioavailabe and this has been proposed to directly feed indigenous microbial communities at high temperatures, providing a link between these abiotic and biotic zones. The overarching research questions in this project are: What is the extent of the deep biosphere close to the temperature limit of life? How is life adapted to high temperatures in an energy-limited habitat? What are the bio-available compounds that are released from the kerogens in sediments with low organic-carbon content and what are the substrates that fuel microbial subseafloor systems close to the temperature limit of life? This proposal intends to implement a comprehensive geochemical approach that will include the quantitative and qualitative downcore analysis of molecular life detection markers such as intact polar lipids and respiratory quinones with ultra-sensitive mass spectrometric techniques. These investigations will be closely coupled to a detailed characterization of the soluble and insoluble organic matter (kerogen). Using elemental, mass spectrometric, spectroscopic and pyrolytic techniques, the quality and bioavailabilty of the kerogen-bound organic matter will be assessed. In addition, the potential for organic substrate generation that may feed the indigenous microbial communities will be tested via hydrous pyrolysis laboratory experiments. This research is directly relevant to fundamental questions of current deep biosphere research and promises to significantly advance our understanding of the extent of the deep subsurface biosphere and the factors which may ultimately limit deeply buried life.