The terrestrial subsurface hosts diverse microbial communities that, collectively, are predicted to comprise as many microbial cells as global surface soils. Although initially thought to be associated with deposited organic matter, contemporary research demonstrates that deep subsurface microbial communities are supported by chemolithoautotrophic primary production, with hydrogen serving as an important source of electrons. Despite recent progress, relatively little is known about the deep terrestrial subsurface compared to more commonly studied environments. Understanding the composition of deep terrestrial subsurface microbial communities and the factors that influence them is of importance because of human-associated activities including long-term storage of used nuclear fuel, carbon capture, and storage of hydrogen for use as an energy vector. In addition to identifying deep subsurface microorganisms, recent research focuses on identifying the roles of microorganisms in subsurface communities, as well as elucidating myriad interactions – syntrophic, episymbiotic, and viral – that occur among community members. In recent years, entirely new groups of microorganisms (i.e., CPR bacteria and DPANN archaea) have been discovered in deep terrestrial subsurface environments, suggesting that much remains unknown about this biosphere. This review explores the historical context for deep terrestrial subsurface microbial ecology and highlights recent discoveries that shape current ecological understanding of this poorly explored microbial habitat. Additionally, we highlight the need for multifaceted experimental approaches to observe phenomena such as cryptic cycles, complex interactions, and episymbiosis, which may not be apparent when using single approaches in isolation, but are nonetheless critical to advancing our understanding of this deep biosphere.

中文翻译：

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陆地深层地下微生物生态学


陆地地下拥有多种微生物群落，预计这些微生物群落的微生物细胞数量与全球表层土壤的微生物细胞数量一样多。尽管最初被认为与沉积的有机物有关，但当代研究表明，深层地下微生物群落受到化能自养初级生产的支持，其中氢是重要的电子来源。尽管最近取得了进展，但与更普遍研究的环境相比，人们对深层陆地地下的了解相对较少。了解深层陆地地下微生物群落的组成以及影响它们的因素非常重要，因为与人类相关的活动包括长期储存用过的核燃料、碳捕获和储存用作能量载体的氢。除了识别深层地下微生物外，最近的研究重点是识别微生物在地下群落中的作用，以及阐明群落成员之间发生的无数相互作用——互养、表共生和病毒。近年来，在陆地深层地下环境中发现了全新的微生物群（即 CPR 细菌和 DPANN 古细菌），这表明关于这个生物圈还有很多未知之处。这篇综述探讨了深层陆地地下微生物生态学的历史背景，并强调了最近的发现，这些发现塑造了当前对这一探索不足的微生物栖息地的生态理解。 此外，我们强调需要多方面的实验方法来观察神秘循环、复杂相互作用和外共生等现象，这些现象在单独使用单一方法时可能并不明显，但对于增进我们对这个深层生物圈的理解至关重要。