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

Exp. 370的目的是探索日本南开海槽Muroto角深海生物圈的最高生命温度，这是一个热流异常高的地点，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°C。这些温度也是发生变质作用的温度，即有机物质热分解为液态和气态碳氢化合物。通过突变反应，假设更不稳定和潜在更氧化的有机物质成为生物可利用性，这已经被提议在高温下直接喂养本地微生物群落，提供这些非生物和生物区域之间的联系。这个项目的首要研究问题是：接近生命温度极限的深层生物圈的程度是多少？生命是如何在能量有限的栖息地适应高温的？在低有机碳含量的沉积物中，从干酪根中释放出的生物可利用化合物是什么？在接近生命极限的温度下，海底微生物系统的燃料是什么？本提案旨在实施一种综合的地球化学方法，包括使用超灵敏质谱技术对分子生命检测标记物（如完整极性脂质和呼吸醌类）进行定量和定性的核心分析。这些研究将与可溶性和不可溶性有机物（干酪根）的详细表征密切相关。利用元素、质谱、光谱和热解技术，将评估干酪根结合有机质的质量和生物利用度。此外，有机底物生成的潜力，可能喂养本地微生物群落将通过水热解实验室实验进行测试。这项研究直接关系到当前深层生物圈研究的基本问题，并有望大大提高我们对深层地下生物圈范围和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.