The icy moons of the outer Solar System harbor potentially habitable environments for life, however, compared to the terrestrial biosphere, these environments are characterized by extremes in temperature, pressure, pH, and other physico-chemical conditions. Therefore, the search for life on these icy worlds is anchored on the study of terrestrial extreme environments (termed “analogue sites”), which harbor microorganisms at the frontiers of polyextremophily. These so-called extremophiles have been found in areas previously considered sterile: hot springs, hydrothermal vents, acidic or alkaline lakes, hypersaline environments, deep sea sediments, glaciers, and arid areas, amongst others. Such model systems and communities in extreme terrestrial environments may provide important information relevant to the astrobiology of icy bodies, including the composition of potential biological communities and the identification of biosignatures that they may produce. Extremophiles can use either sunlight (phototrophs) or chemical energy (chemotrophs) as energy sources, and different chemical compounds as electron donors or acceptors. Aerobic microorganisms use oxygen (O 2 ) as a terminal electron acceptor, whereas anaerobic microorganisms may use nitrate ( NO 3 − $\mathrm{NO}_{3} ^{-}$ ), sulfate ( SO 4 2 − $\mathrm{SO}_{4} ^{2-}$ ), carbon dioxide (CO 2 ), Fe(III), or other organic or inorganic molecules during respiration. The phylogenetic diversity of extremophiles is very high, leading to their broad dispersal across the phylogenetic tree of life together with a wide variety in metabolic diversity. Some metabolisms are specific to archaea, for example, methanogenesis, an anaerobic respiration during which methane (CH 4 ) is produced. Also sulfur-reduction performed by some bacteria and archaea is considered as a primitive metabolism which is restricted to anoxic sulfur-rich habitats in nature. Methanogenesis and sulfur reduction are of specific interest for icy moon research as it might be one of the few known terrestrial metabolisms possible on these celestial bodies. Therefore, the adaptation of these intriguing microorganisms to extreme conditions will be highlighted within this review.

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微生物多样性和生物特征：冰冷的卫星视角

太阳系外冰冷的卫星为生命提供了潜在的宜居环境，然而，与陆地生物圈相比，这些环境的特点是温度、压力、pH 值和其他物理化学条件极端。因此，在这些冰冷的世界上寻找生命的基础是对陆地极端环境（称为“类似地点”）的研究，这些环境在多极端性的前沿拥有微生物。这些所谓的极端微生物已在以前被认为是无菌的地区发现：温泉、热液喷口、酸性或碱性湖泊、高盐环境、深海沉积物、冰川和干旱地区等。极端陆地环境中的此类模型系统和群落可能会提供与冰天体的天体生物学相关的重要信息，包括潜在生物群落的组成以及它们可能产生的生物特征的识别。极端微生物可以使用阳光（光养生物）或化学能（化学营养生物）作为能源，使用不同的化合物作为电子供体或受体。好氧微生物使用氧气 (O 2 ) 作为终端电子受体，而厌氧微生物可能使用硝酸盐 ( NO 3 − $\mathrm{NO}_{3} ^{-}$ )、硫酸盐 ( SO 4 2 − $\mathrm {SO}_{4} ^{2-}$ )、二氧化碳 (CO 2 )、Fe(III) 或其他有机或无机分子在呼吸过程中。极端微生物的系统发育多样性非常高，导致它们在生命的系统发育树中广泛分布，代谢多样性也多种多样。一些代谢是古细菌特有的，例如产甲烷、产生甲烷 (CH 4 ) 的无氧呼吸。此外，一些细菌和古细菌进行的硫还原被认为是一种原始代谢，仅限于自然界中缺氧的富含硫的栖息地。甲烷生成和硫还原是冰月研究的特别关注点，因为它可能是这些天体上为数不多的已知陆地代谢之一。因此，本文将重点介绍这些有趣的微生物对极端条件的适应性。甲烷生成和硫还原是冰月研究的特别关注点，因为它可能是这些天体上为数不多的已知陆地代谢之一。因此，本文将重点介绍这些有趣的微生物对极端条件的适应性。甲烷生成和硫还原是冰月研究的特别关注点，因为它可能是这些天体上为数不多的已知陆地代谢之一。因此，本文将重点介绍这些有趣的微生物对极端条件的适应性。