Biosignatures of microbial function in subsurface systems

微生物是地球上最早的生命形式，现在仍然是最丰富的生命形式，并且被认为是在寻找地球以外生命时最可能观察到的生命形式。了解极端环境中与微生物生命相关的独特有机、同位素、矿物或形态生物特征，为我们解释地质记录中记录的地球生命历史提供了基础，也为我们在火星或其他地方寻找生命提供了基础。据估计，地下生物圈的质量与地球表面相当，但直到最近才开始探索。本提案旨在了解与陆地深层地下生命相关的碳源、代谢活动和生物特征，并将其与极端环境下生活在岩石表面以下的内石器群落进行比较和对比。利用正在进行的研究和与工作矿山的关系，这项研究将对裂缝系统进行采样，范围从在较浅深度隔离了数千年至数百万年的古陨石生物系统到已经隔离了超过10亿年的古代深层系统，这些系统可能保存了与早期地球和陨石相当的非生物特征。细菌、真核生物和古细菌的生物特征，以及细菌孢子形成的特征将在这些系统中进行分析，以评估微生物群落，包括微生物丰度的分布、支持它的碳源和循环、其持久性的限制以及它在地质时间尺度上是一个动态系统的程度。识别和解释地球上以及潜在的其他地方的微生物生命活动的证据，还需要能够区分生命及其过程的独特“生物特征”与非生物系统的特征（“非生物特征”）。虽然生命在地球上几乎所有的环境中都覆盖了任何非生物特征，但这些深层裂缝系统中的一些，尤其是最古老的，实际上可能是对非生物条件的采样，因此提供了一个无与伦比的机会来表征地球上的“非生物特征”。然后，这些非生物特征可以与陨石相关的特征进行比较，并为寻找地外生命提供令人兴奋的新视角。除了现场样品外，设计用于表征微生物利用水岩相互作用产生的能量和/或碳源的生物特征的微观实验将用于生成基于实验室的数据集，这将有助于解释现场结果。作为对这种深层地下系统的反击，第二个研究重点将是在极端干旱、温度和地球化学的表面环境中生活在岩石表面以下几毫米处的内石器群落。了解这些系统的丰度、代谢和持久性将有助于深入地下研究，进一步了解生命的极限和能力，以及发展我们对生物特征的理解及其对地球生命地质记录中的生命记录的影响，并作为寻找其他行星生命的目标。

Microbial organisms were the first and remain the most prolific forms of life on Earth, and are thought to be the most likely form of life to be observed in the search for life beyond the Earth. Understanding the unique organic, isotopic, mineral or morphologic biosignatures associated with microbial life in extreme environments provides the foundation for our interpretation of the history of life on Earth recorded in the geologic record, as well as the basis by which we will search for life on Mars or elsewhere. While estimated to be comparable in mass to that on Earth’s surface, the subsurface biosphere is only recently being explored. This proposal seeks to understand the carbon sources, metabolic activities and biosignatures associated with life in the deep terrestrial subsurface, and to compare and contrast it with those of endolithic communities living just below the surface of rocks in extreme environments. Taking advantage of ongoing research and relationships with working mines, this research will sample fracture systems that range from paleometeoric, biological systems isolated for thousands to millions of years at shallower depths to ancient, deeper systems that have been isolated for up to more than a billion years and may preserved abiotic signatures comparable to the early Earth and meteorites. Biosignatures of bacteria, eukarya and archea, as well as signatures of bacterial spore formation will be analyzed across these systems to assess the microbial community including the distribution of microbial abundance, the carbon sources and cycling that is supporting it, and the limits on its persistence along with the extent to which it is a dynamic system over geologic timescales. Recognizing and interpreting evidence of the activities of microbial life, both on Earth and potentially beyond, also requires the ability to differentiate unique “biosignatures” of life and its processes from signatures of abiotic systems (“abiosignatures”). While life has overprinted any abiotic signatures in almost all environments on Earth, some of these deep fracture systems, especially the most ancient ones, may in fact sample abiotic conditions and thus provide an unparalleled opportunity to characterize “abiosignatures” on Earth. These abiosignatures could then be compared to those associated with meteorites and provide an exciting new perspective on the search for life beyond the Earth. In addition to field samples, microcosm experiments designed to characterize biosignatures of microbial utilization of energy and/or carbon sources generated via water rock interaction will be used generate an laboratory based dataset that will contribute to interpretation of field results. As a counter point to this deep subsurface system, a secondary research focus will be on endolithic communities living millimeters below the surface of rocks in surface environments under extremes of aridity, temperature and geochemistry. Understanding the abundance, metabolisms and persistence of these systems will contribute complimentary insight to the research in the deep subsurface, furthering our understanding of the limits and capabilities of life, as well as developing our understanding of biosignatures and their implications to the record of life in the geologic record of life on Earth and as targets for the search for life on other planets.