Havig Jeff R, Kuether Joshua E, Gangidine Andrew J, Schroeder Sarah, Hamilton Trinity L
Department of Earth and Environmental Sciences, University of Minnesota, Minneapolis, Minnesota, USA.
Department of Plant and Microbial Biology, University of Minnesota, Saint Paul, Minnesota, USA.
Astrobiology. 2021 Dec;21(12):1526-1546. doi: 10.1089/ast.2019.2086.
Hydrothermal systems host microbial communities that include some of the most deeply branching members of the tree of life, and recent work has suggested that terrestrial hot springs may have provided ideal conditions for the origin of life. Hydrothermal microbial communities are a potential source for biosignatures, and the presence of terrestrial hot spring deposits in 3.48 Ga rocks as well as on the surface of Mars lends weight to a need to better understand the preservation of biosignatures in these systems. Although there are general patterns of elemental enrichment in hydrothermal water dependent on physical and geochemical conditions, the elemental composition of bulk hydrothermal microbial communities (here termed biocumulus, including cellular biomass and accumulated non-cellular material) is largely unexplored. However, recent work has suggested both bulk and spatial trace element enrichment as a potential biosignature in hot spring deposits. To elucidate the elemental composition of hot spring biocumulus samples and explore the sources of those elements, we analyzed a suite of 16 elements in hot spring water samples and corresponding biocumulus from 60 hot springs sinter samples, and rock samples from 8 hydrothermal areas across Yellowstone National Park. We combined these data with values reported in literature to assess the patterns of elemental uptake into biocumulus and retention in associated siliceous sinter. Hot spring biocumuli are of biological origin, but organic carbon comprises a minor percentage of the total mass of both thermophilic chemotrophic and phototrophic biocumulus. Instead, the majority of hot spring biocumulus is inorganic material-largely silica-and the distribution of major and trace elements mimics that of surrounding rock and soil rather than the hot spring fluids. Analyses indicate a systematic loss of biologically associated elements during diagenetic transformation of biocumulus to siliceous sinter, suggesting a potential for silica sinter to preserve a trace element biosignature.
热液系统中存在着微生物群落，其中包括一些生命之树上分支最深的成员，最近的研究表明，陆地温泉可能为生命起源提供了理想条件。热液微生物群落是生物标志物的潜在来源，34.8亿年前岩石以及火星表面存在陆地温泉沉积物，这使得我们更有必要深入了解这些系统中生物标志物的保存情况。尽管热液水中的元素富集存在一般模式，这取决于物理和地球化学条件，但热液微生物群落整体（这里称为生物堆积物，包括细胞生物质和积累的非细胞物质）的元素组成在很大程度上尚未得到探索。然而，最近的研究表明，整体和空间微量元素富集是温泉沉积物中一种潜在的生物标志物。为了阐明温泉生物堆积物样本的元素组成并探究这些元素的来源，我们分析了黄石国家公园8个热液区域的60个温泉硅华样本中的温泉水样、相应的生物堆积物以及岩石样本中的16种元素。我们将这些数据与文献报道的值相结合，以评估元素被生物堆积物吸收以及在相关硅质硅华中保留的模式。温泉生物堆积物源自生物，但有机碳在嗜热化学营养型和光合营养型生物堆积物的总质量中占比很小。相反，温泉生物堆积物的大部分是无机物质——主要是二氧化硅——主要和微量元素的分布与周围岩石和土壤相似，而非温泉流体。分析表明，在生物堆积物成岩转化为硅质硅华的过程中，与生物相关的元素会系统性流失，这表明硅质硅华有可能保存微量元素生物标志物。
