CARBON ISOTOPIC SIGNATURES OF MICROBIAL LIPIDS IN GEOTHERMAL DEPOSITS: ELUCIDATING THERMOPHILIC ECOLOGY

了解生命的起源和多样性是最具挑战性的科学努力之一。在这种努力中，限制地球上生命的界限至关重要，了解那些能够在极端温度、盐度或pH的环境中生存甚至繁衍的生物的生态也是至关重要的。特别令人感兴趣的是地热系统，由各种分支的嗜热菌和古生菌组成。最近，我们证明了微生物脂类是评估和重建陆地温泉微生物学的有力工具。在这项建议中，我们重点阐明地热生物体类脂的碳同位素特征。脂质生物标记物的使用与稳定同位素分析相结合对于理解微生物生态学是至关重要的，它提供了微生物鉴定和生化过程之间的直接联系。脂肪存在于所有活的生物体中，通常作为细胞膜的能源和结构成分。这些化合物通常具有很高的诊断性，在地质记录中保存完好，并含有关于生物多样性、环境条件和沉积后蚀变历史的信息，对于早期生命和天体生物学研究特别有吸引力。我们过去对地热矿床中生物标志物的研究揭示了包裹性脂类的深刻多样性，这可以用来描述微生物群落组成。然而，我们之前的工作尚未开发的微生物保存脂类的潜力是它们的碳同位素组成；在我们的一小部分数据中观察到脂类碳同位素值强烈和非常不寻常的变化，但缺乏关键的上下文数据(例如，池中溶解的无机碳的碳同位素组成，DIC)。这仍然是关于新西兰陶波火山带的嗜热生理和生态以及那里形成的二氧化硅矿床的一个未开发的信息来源。这些矿床是前世生活的重要档案，阐明在这种环境下对有机质形成的控制将允许更好地解释保存在其中的OM组合。我们将绘制碳同位素值范围图，并评估其在不同物理化学条件和不同生物相中的重现性。通过将这些数据嵌入到温泉DIC碳同位素值和最近基于分子(DNA和RNA)方法的微生物群落概况中，我们将解决异常碳同位素组成的来源。这将极大地扩展我们解释保存在古代硅质烧结矿中的生物标志物碳同位素值的能力，提供关于脂肪生物标志物来源、新陈代谢和营养结构的关键信息。在这项工作中，我们将针对新西兰陶波火山带特征良好的地热环境中的一系列诊断化合物，探索碳同位素特征变化的控制，将我们过去基于生物标志物的解释与碳同位素分析结合起来，以便更好地了解地热环境的生物多样性，并揭示生物地球化学和生态功能。这项工作将推进我们对保存在岩石记录中的生物特征的解释，提供对地球上最早的生命形式的进化和生态的洞察，并为在太阳系其他地方寻找生命提供信息。

Understanding the origins and diversification of life represents one of the most challenging scientific endeavours. In such efforts, constraining the limits of life on Earth is vital, as is an understanding of the ecology of those organisms that can survive and even thrive in environments characterised by extremes of temperature, salinity or pH. Of particular interest are geothermal systems, populated by diverse and deeply-branching thermophilic bacteria and Archaea. Recently we have demonstrated that microbial lipids are powerful tools in assessing and reconstructing the microbiology of terrestrial hot springs. In this proposal we focus on elucidating the carbon isotopic signatures of the lipids of geothermal organisms. The use of lipid biomarkers in combination with stable isotope analysis is crucial to understanding microbial ecology, providing a direct link between microbial identity and biochemical processes.Lipids are found in all living organisms, typically serving as energy sources and structural components of cell membranes. Often highly diagnostic, well-preserved in the geological record, and entrained with information on biological diversity, environmental conditions and post-depositional alteration history, these compounds are particularly attractive for early life and astrobiological investigations. Our past studies of biomarkers in geothermal deposits reveal a profound diversity of encapsulated lipids, which can be utilized to profile microbial community composition. However, a potential of microbialite-preserved lipids that was untapped by our previous work is their carbon isotopic composition; strong and highly unusual variations in lipid carbon isotope values were observed in a small subset of our data but lacked crucial contextual data (e.g. the carbon isotopic composition of dissolved inorganic carbon, DIC, in the pools). This remains an untapped source of information on thermophilic physiologies and ecology in the New Zealand Taupo Volcanic Zone and the silica deposits formed there. Such deposits are essential archives of past life and elucidating the controls on organic matter formation in such settings will allow a better interpretation of the OM assemblages preserved in them. We will map the range of carbon isotope values and evaluate their reproducibility in various geothermal sites with differing physicochemical conditions and in different biofacies. By embedding this data in the context of thermal spring DIC carbon isotope values and recent microbiological community profiling based on molecular (DNA and RNA) approaches, we will resolve the origin of the unusual carbon isotopic compositions. This will greatly expand on our capacity to interpret biomarker carbon isotope values preserved in ancient silica sinters, providing crucial information on sources of lipid biomarkers, metabolism and trophic structure. In this work, we will target a range of diagnostic compounds from well-characterized geothermal settings in the Taupo Volcanic Zone in New Zealand and explore the controls on the variation of carbon isotopic signatures, coupling our past biomarker-based interpretations to carbon isotopic analyses in order to achieve a better understanding of the biodiversity of geothermal environments and to unravel biogeochemical and ecological function. This work will advance our interpretation of biosignatures preserved in the rock record, providing insight into the evolution and ecology of the earliest life-forms on Earth and informing the search for life elsewhere in the Solar System.