High Throughput Technique for Screening Archaeal Tetraether Lipid Cores in Sediments as Probes of Palaeo Surface-water Temperature

古生菌是生命的三大领域之一，长期以来一直被认为局限于极端的温度、pH值、盐度和缺氧环境。自20世纪90年代初发现海洋中的古细菌基因序列以来，非极端古细菌已被证明在海洋中普遍存在，它们在碳和氮循环中发挥着重要作用。这些生物对海洋元素循环的长期贡献可以从对脂质结构的识别中看出，这些脂质结构是古细菌特有的，来自于大约9000万年前沉积的沉积物中的膜。在只有古细菌产生的脂质中，在这些膜脂源成分中包含的五元环的数量不同。环数的差异被认为调节了膜的组织，使生物体适应不同的条件，例如它们生长的温度。一个特定的比率（TEX86指数）是根据海洋沉积物中存在的五元环的不同数量的结构的比例计算出来的，它与上覆海洋的表面水温有很强的相关性，这为从沉积物岩心中保存的古细菌脂质残留物的分析中得出过去海洋表面水温提供了可能。进一步的研究已经确定了TEX86指数与地表水温度呈线性趋势的情况，但该值被若干摄氏度抵消。我们之前已经展示了一种使用串联质谱法区分不同古菌脂质结构的方法，并揭示了用于TEX86指数测量的一些色谱峰包含异构结构。我们计划区分单个脂质结构，包括异构体，使用改进的分离和串联质谱的应用相结合。因此，我们将获得更完善的TEX86测量。同时，我们计划解决分析方法中可以引入新策略的问题，以提高检测极低水平化合物的能力和获得TEX86值的整体技术的速度。因此，我们计划开发一种高通量技术，该技术将提供过去使用非常小的沉积物样本量和非常短的分析时间来评估海洋表面水温的能力。这将使温度记录能够以非常高的深度分辨率生成，允许数据具有高时间分辨率，从而即使在短时间间隔内也能显示温度变化。生成温度变化的密集记录的能力将对关注了解过去时代海洋环境的性质及其对环境压力的反应的研究人员以及开发与最近地质过去（第四纪）的气候变化有关的更清晰的记录有相当大的好处。该方法也可应用于评估脂质长期稳定性的古代沉积物序列。

Archaea, one of the three domains of life, were long considered to be limited to environments that exhibit extremes of temperature, pH, salinity and anoxia. Since the recognition, in the early 1990's, of archaeal gene sequences in the oceans, non-extreme archaea have been shown to be prevalent in the oceans where they fulfill important roles in the carbon and nitrogen cycles. The long term contribution of these organisms to marine element cycling is evident from the recognition of lipid structures, that are specific to the archaea and derive from their membranes, in sediments deposited around 90 million years ago. Among the lipids produced only by the archaea are structures that differ in the number of five-membered rings contained within these membrane lipid-derived components. The differences in the number of rings are believed to regulate the organisation of the membrane, allowing the organisms to adapt to different conditions, e.g. temperature, under which they grow. A particular ratio (the TEX86 index) computed from the proportions of structures with different numbers of five-membered rings that are present in marine sediments was shown to correlate very strongly with the surface water temperature of the overlying ocean, providing the potential to derive sea surface water temperatures of oceans in times past from analysis of the archaeal lipid residues preserved within sediment cores. Further investigations have identified situations where the TEX86 index shows linear trends with surface water temperature, but the values are offset by a number of degrees C. We have previously demonstrated a method using tandem mass spectrometry that differentiates different archaeal lipid structures and reveals that some of the chromatographic peaks measured for use in the TEX86 index contain isomeric structures. We plan to differentiate individual lipid structures, including isomers, using a combination of improved separation and application of tandem mass spectrometry. Hence, we will obtain much improved measurements of TEX86. At the same time, we plan to address points in the analytical approach where new strategies can be introduced to improve both the capability to detect compounds at very low levels and the speed of the overall technique for deriving the TEX86 values. Thus, we plan to develop a high throughput technique that will deliver the capacity to assess sea surface water temperatures in the past using very small sediment sample sizes and with very short analysis times. This will enable the temperature records to be generated at very high depth resolution, allowing high time resolution in the data and thereby revealing changes in temperature even over short intervals of time. The ability to generate intensive records of temperature change will be of considerable benefit to researchers concerned with understanding the nature of the marine environment in times past and its response to environmental stresses, and in developing clearer records that relate to climate change over the recent geological past (Quaternary). The method may also have application to ancient sediment sequences subject to assessment of the longer-term stability of the lipids.