Table_2_Lipid Profiles From Fresh Biofilms Along a Temperature Gradient on a Hydrothermal Stream at El Tatio (Chilean Andes), as a Proxy for the Interpretation of Past and Present Biomarkers Beyond Earth.XLSX

Hydrothermal systems and their deposits are primary targets in the search for fossil evidence of life beyond Earth. However, to learn how to decode fossil biomarker records in ancient hydrothermal deposits, we must first be able to interpret unambiguously modern biosignatures, their distribution patterns, and their association with physicochemical factors. Here, we investigated the molecular and isotopic profile of microbial biomarkers along a thermal gradient (from 29 to 72°C) in a hot spring (labeled Cacao) from El Tatio, a geyser field in the Chilean Andes with abundant opaline silica deposits resembling the nodular and digitate structures discovered on Mars. As a molecular forensic approach, we focused on the analysis of lipid compounds bearing recognized resistance to degradation and the potential to reconstruct the paleobiology of an environment on a broader temporal scale than other, more labile, biomolecules. By exploiting the lipid biomarkers’ potential to diagnose biological sources and carbon fixation pathways, we reconstructed the microbial community structure and its ecology along the Cacao hydrothermal transect. The taxonomic adscription of the lipid biomarkers was qualitatively corroborated with DNA sequencing analysis. The forensic capacity of the lipid biomarkers to identify biosources in fresh biofilms was validated down to the genus level for Roseiflexus, Chloroflexus, and Fischerella. We identified lipid biomarkers and DNA of several new cyanobacterial species in El Tatio and reported the first detection of Fischerella biomarkers at a temperature as high as 72°C. This, together with ecological peculiarities and the proportion of clades being characterized as unclassified, illustrates the ecological singularity of El Tatio and strengthens its astrobiological relevance. The Cacao hydrothermal ecosystem was defined by a succession of microbial communities and metabolic traits associated with a high- (72°C) to low-(29°C) temperature gradient that resembled the inferred metabolic sequence events from the 16S rRNA gene universal phylogenetic tree from thermophilic to anoxygenic photosynthetic species and oxygenic phototrophs. The locally calibrated DNA-validated lipidic profile in the Cacao biofilms provided a modern (molecular and isotopic) end member to facilitate the recognition of past biosources and metabolisms from altered biomarkers records in ancient silica deposits at El Tatio analogous to Martian opaline silica structures.

热液系统（hydrothermal systems）及其沉积体是搜寻地外生命化石证据的核心靶标。然而，若要解读古热液沉积中的化石生物标志物（biomarker）记录，我们首先需明确阐释现代生物标志物的特征、分布规律及其与物理化学因素的关联。本研究针对智利安第斯山脉间歇泉田埃尔塔蒂奥（El Tatio）一处命名为可可（Cacao）的热泉展开了梯度调查，该热泉产出的蛋白石硅质沉积与火星上发现的结核状、指状构造高度相似，其水温梯度覆盖29℃至72℃。作为一种分子溯源方法，我们聚焦于抗降解能力强、相较于其他易降解生物分子更适用于更长时间尺度环境古生物学重建的脂质化合物分析。通过利用脂质生物标志物识别生物来源与固碳途径的潜力，我们重构了可可热泉断面的微生物群落结构及其生态特征。脂质生物标志物的分类学归属通过DNA测序分析得到了定性验证。该脂质生物标志物用于识别新鲜生物膜中生物来源的溯源能力，在玫瑰线菌属（Roseiflexus）、绿弯菌属（Chloroflexus）与费氏蓝细菌属（Fischerella）的属级水平上得到了验证。我们在埃尔塔蒂奥中发现了多种新的蓝细菌（cyanobacterium）物种的脂质生物标志物与DNA，并首次报道了在72℃高温环境下检出费氏蓝细菌属生物标志物的结果。这一发现，结合该区域的生态特殊性以及未分类进化枝的占比，凸显了埃尔塔蒂奥的生态独特性，并进一步强化了其天体生物学（astrobiology）研究价值。可可热泉生态系统以沿高温（72℃）至低温（29℃）温度梯度分布的微生物群落演替与代谢特征为核心特征，其演替序列与基于16S核糖体RNA基因（16S rRNA gene）通用系统发育树推断的从嗜热菌、不产氧光合生物到产氧光合生物的代谢事件序列高度一致。本研究在可可热泉生物膜中通过DNA验证得到的本地化校准脂质组学特征，可为解读埃尔塔蒂奥古硅质沉积（与火星蛋白石硅质构造类似）中经改造的生物标志物记录、识别其古老生物来源与代谢过程提供现代（分子与同位素）基准端元。