Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China.
France-China Joint Laboratory for Evolution and Development of Magnetotactic Multicellular Organisms, Chinese Academy of Sciences, 100029, Beijing, China.
ISME J. 2023 Oct;17(10):1526-1534. doi: 10.1038/s41396-023-01495-w. Epub 2023 Aug 17.
Capable of forming magnetofossils similar to some magnetite nanocrystals observed in the Martian meteorite ALH84001, magnetotactic bacteria (MTB) once occupied a special position in the field of astrobiology during the 1990s and 2000s. This flourish of interest in putative Martian magnetofossils faded from all but the experts studying magnetosome formation, based on claims that abiotic processes could produce magnetosome-like magnetite crystals. Recently, the rapid growth in our knowledge of the extreme environments in which MTB thrive and their phylogenic heritage, leads us to advocate for a renaissance of MTB in astrobiology. In recent decades, magnetotactic members have been discovered alive in natural extreme environments with wide ranges of salinity (up to 90 g L), pH (1-10), and temperature (0-70 °C). Additionally, some MTB populations are found to be able to survive irradiated, desiccated, metal-rich, hypomagnetic, or microgravity conditions, and are capable of utilizing simple inorganic compounds such as sulfate and nitrate. Moreover, MTB likely emerged quite early in Earth's history, coinciding with a period when the Martian surface was covered with liquid water as well as a strong magnetic field. MTB are commonly discovered in suboxic or oxic-anoxic interfaces in aquatic environments or sediments similar to ancient crater lakes on Mars, such as Gale crater and Jezero crater. Taken together, MTB can be exemplary model microorganisms in astrobiology research, and putative ancient Martian life, if it ever occurred, could plausibly have included magnetotactic microorganisms. Furthermore, we summarize multiple typical biosignatures that can be applied for the detection of ancient MTB on Earth and extraterrestrial MTB-like life. We suggest transporting MTB to space stations and simulation chambers to further investigate their tolerance potential and distinctive biosignatures to aid in understanding the evolutionary history of MTB and the potential of magnetofossils as an extraterrestrial biomarker.
能够形成类似于火星陨石 ALH84001 中观察到的一些磁铁矿纳米晶体的磁化石的趋磁细菌 (MTB)，在 20 世纪 90 年代和 21 世纪初的天体生物学领域占据了特殊地位。由于声称非生物过程可以产生类似磁小体的磁铁矿晶体，因此对假定的火星磁化石的兴趣除了研究磁小体形成的专家之外，几乎都消失了。最近，我们对 MTB 赖以生存的极端环境及其系统发育遗产的了解迅速增加，这促使我们主张在天体生物学中重新研究 MTB。在过去的几十年中，在具有广泛盐度（高达 90 g/L）、pH 值（1-10）和温度（0-70°C）的自然极端环境中发现了活体趋磁细菌成员。此外，一些 MTB 种群被发现能够在辐照、干燥、富含金属、低磁或微重力条件下生存，并能够利用简单的无机化合物，如硫酸盐和硝酸盐。此外，MTB 可能在地球历史的早期就已经出现，这与火星表面被液态水以及强磁场覆盖的时期相吻合。MTB 通常在水生环境或沉积物的缺氧或有氧-缺氧界面中发现，类似于火星上的古老陨石坑湖，如盖尔陨石坑和杰泽罗陨石坑。综上所述，MTB 可以成为天体生物学研究中典型的模式微生物，如果曾经存在过古代火星生命，那么很可能包括趋磁微生物。此外，我们总结了多个可用于检测地球和外星 MTB 样生命的典型生物特征。我们建议将 MTB 运送到空间站和模拟室，以进一步研究它们的耐受潜力和独特的生物特征，以帮助理解 MTB 的进化历史和磁化石作为外星生物标志物的潜力。
