Institute of Marine and Environmental Technology, University of Maryland School of Medicine, Baltimore, MD, USA.
Department of Earth and Planetary Sciences, University of California, Riverside, CA, USA.
Extremophiles. 2020 Jan;24(1):31-41. doi: 10.1007/s00792-019-01126-3. Epub 2019 Aug 28.
Recent progress in extremophile biology, exploration of planetary bodies in the solar system, and the detection and characterization of extrasolar planets are leading to new insights in the field of astrobiology and possible distribution of life in the universe. Among the many extremophiles on Earth, the halophilic Archaea (Haloarchaea) are especially attractive models for astrobiology, being evolutionarily ancient and physiologically versatile, potentially surviving in a variety of planetary environments and with relevance for in situ life detection. Haloarchaea are polyextremophilic with tolerance of saturating salinity, anaerobic conditions, high levels of ultraviolet and ionizing radiation, subzero temperatures, desiccation, and toxic ions. Haloarchaea survive launches into Earth's stratosphere encountering conditions similar to those found on the surface of Mars. Studies of their unique proteins are revealing mechanisms permitting activity and function in high ionic strength, perchlorates, and subzero temperatures. Haloarchaea also produce spectacular blooms visible from space due to synthesis of red-orange isoprenoid carotenoids used for photoprotection and photorepair processes and purple retinal chromoproteins for phototrophy and phototaxis. Remote sensing using visible and infrared spectroscopy has shown that haloarchaeal pigments exhibit both a discernable peak of absorption and a reflective "green edge". Since the pigments produce remotely detectable features, they may influence the spectrum from an inhabited exoplanet imaged by a future large space-based telescope. In this review, we focus primarily on studies of two Haloarchaea, Halobacterium sp. NRC-1 and Halorubrum lacusprofundi.
近年来，极端生物学生物学、太阳系行星体的探索以及系外行星的探测和特征描述，为天体生物学领域带来了新的见解，并可能揭示了宇宙中生命的分布。在地球上的许多极端生物中，嗜盐古菌（Haloarchaea）是天体生物学中特别有吸引力的模型，因为它们具有古老的进化历史和多功能的生理学特性，有可能在各种行星环境中生存，并与原位生命探测有关。嗜盐古菌是多极端环境耐受的，可以耐受饱和盐度、厌氧条件、高强度紫外线和电离辐射、零下温度、干燥和有毒离子。嗜盐古菌可以在进入地球平流层时幸存下来，遇到的条件类似于火星表面的条件。对它们独特蛋白质的研究揭示了在高离子强度、高氯酸盐和零下温度下允许活性和功能的机制。嗜盐古菌还会产生壮观的生物发光现象，从太空中可见，这是由于合成用于光保护和光修复过程的红色橙色类异戊二烯类胡萝卜素和用于光营养和趋光性的紫色视网膜色氨酸所致。可见光和红外光谱的遥感表明，嗜盐古菌的色素既具有可识别的吸收峰，又具有反射性的“绿色边缘”。由于这些色素可以产生远程可检测的特征，它们可能会影响未来大型空间望远镜拍摄的可居住系外行星的光谱。在这篇综述中，我们主要关注两种嗜盐古菌，即 Halobacterium sp. NRC-1 和 Halorubrum lacusprofundi 的研究。
