Characterizing unexplored microbial habitats in oceanic crust along the South Atlantic Transect, IODP Exp. 390/393

该提案寻求资金用于IODP Exp期间回收的样本的工作。390/393“南大西洋断面”(SAT)，在缓慢扩张的中大西洋中脊的西侧，钻取了一段约7~61 Ma的玄武岩地壳。SAT的主要目标是促进我们对海脊侧面热液-岩石反应以及伴随而来的洋壳内微生物生命的分布和环境控制的了解。该项目将利用有机地球化学与岩石学调查相结合的跨学科方法直接处理这些问题，以研究以前未被勘探的洋壳内的地壳微生物栖息地。拟议的工作将集中在已发现的沉积角砾岩上，除了在61 Ma老遗址U1557异常恢复的最年轻地点。类似的角砾岩在世界各地的各种海洋大地构造环境中都存在。因此，我们假定角砾岩是地壳深层生物圈中一个重要但迄今被忽视的组成部分。高渗透性的岩石为流体流动提供了充足的路径，从而为流体-岩石反应提供了充足的路径，而流体-岩石反应反过来又提供了生物燃料，从而培育了微生物生命。在第一步中，我们计划将对回收的角砾岩进行的类脂生物标志物调查与确定岩石蚀变的程度和类型相结合。在第二步中，地壳岩石的氧化状态将允许估计微生物生物量生产的生物可用能量，然后我们将与脂肪生物量的实际分布相关联。脂类的详细结构特征将能够评估微生物群落的多样性如何受到底物年龄的增加的影响，并将确定对各自生境的生理适应。化合物特定的稳定碳同位素将被用来确定潜在的微生物代谢从化学自养向异养生活方式的转变，后者可能在更老、更氧化、因此产生能量更少的岩石中占优势。最后，利用最先进的质谱学成像技术结合显微XRF，将微生物生命热点在微米尺度上可视化，并与角砾岩的宿主矿物基质建立空间关系。因此，该项目有望为目前地壳深层生物圈研究的知识空白提供令人振奋的新见解，并通过挖掘角砾状海底的未探索地壳栖息地，将有助于改进对深层生物圈的估计，并大大促进我们对地球假定的最大微生物群的了解。

This proposal seeks funding to work on samples recovered during IODP Exp. 390/393 "South Atlantic Transect" (SAT), during which a transect from ~7 to 61 Ma old basaltic crust was drilled at the western ridge flank of the slow-spreading southern Mid-Atlantic Ridge. The primary goals of SAT were to further our understanding of ridge flank hydrothermal fluid–rock reactions and concomitant distributions and environmental controls of microbial life within the oceanic crust. This project will directly address these topics by using an interdisciplinary approach combining organic geochemical with petrological investigations to examine a previously unexplored crustal microbial habitat within the ocean crust. The proposed work will focus on sedimentary breccias that were recovered at all except the youngest sites with exceptional recovery at 61 Ma old Site U1557. Similar breccias occur worldwide in a variety of oceanic geotectonic settings. We therefore postulate that breccias constitute an important, but so far overlooked component of the crustal deep biosphere. The highly permeable rocks provide ample paths for fluid flow and hence for fluid-rock reactions, which in turn provides biofuels and hence fosters microbial life. In a first step we plan to combine lipid biomarker investigations of the recovered breccias with determining the extent and style of rock alteration. In a second step, the oxidation state of the crustal rocks will allow the estimation of bioavailable energy for microbial biomass production, which we will then relate to the actual distribution of lipid biomass. Detailed structural characterization of lipids will allow the assessment of how the diversity of microbial communities is affected by the increasing substrate age and will identify physiologic adaptations to the respective habitats. Compound specific stable carbon isotopes will be used to determine potential microbial metabolism shifts from chemolithoautotrophic to heterotrophic lifestyles, the latter of which may prevail in older, more oxidized and hence less energy-yielding rocks. Finally, hot spots of microbial life will be visualized and put into spatial relation with the host mineral matrix of the breccias on a micrometer scale by making use of state-of-the-art mass spectrometry imaging combined with micro-XRF. This project thus promises to provide exciting new insights into current knowledge gaps of deep crustal biosphere research and by tapping into the unexplored crustal habitat of brecciated seafloor, will help refine estimates of the deep biosphere and significantly advance our understanding of Earth’s presumed largest microbiome.