Groninga Janina, Lipp Julius, Song Min, Hinrichs Kai-Uwe
MARUM - Center for Marine Environmental Sciences, and Faculty of Geosciences, University of Bremen, Bremen, Germany.
Department of Earth Sciences, University of Toronto, Toronto, Ontario, Canada.
Rapid Commun Mass Spectrom. 2025 Nov 30;39(22):e10118. doi: 10.1002/rcm.10118.
The stable carbon isotopic composition (δC) of individual lipids is of great value in studying carbon cycling. Among those, microbial lipids in sediments impacted by high methane turnover stand out due to their uniquely depleted isotopic fingerprint. However, gas chromatography/isotope ratio mass spectrometry (GC/irMS) is limited to volatile compounds, whereas intact polar lipids require extensive preprocessing, which results in the loss of chemotaxonomic information. Expanding compound-specific isotopic information to intact polar lipids would enhance insights into the microbial turnover of methane.
We performed ultra-high-performance liquid chromatography/electrospray ionization/high-resolution mass spectrometry (UHPLC/ESI/HRMS) to analyze standards of archaeol and lipid extracts from a diverse set of sediment samples of a hydrothermal methane seep system. Using the ratio of the M1 isotopologue over the monoisotopic isotopologue M0, we calculated the δC values of archaeol and various polar, non-GC-amenable lipids. The δC values of archaeol obtained via ratios were compared to those measured via GC/irMS.
δC values of archaeol determined in natural samples via GC/irMS and the UHPLC/HRMS approach were strongly correlated (R = 0.94; N = 76-82) across a wide range of δC values (GC-irMS = -119‰ to -34‰). Biomarkers associated with methane turnover consistently yielded δC values below -60‰, whereas the δC values of compounds presumably associated with the photosynthesis-based food web remained above -45‰. UHPLC/HRMS measurements of archaeol standard further indicated that δC values can be reliably determined across an M0 signal-intensity range of approximately one order of magnitude.
Our results highlight that the M1/M0 ratio from UHPLC/HRMS measurements can be utilized to evaluate the carbon isotopic fingerprint of non-GC-amenable lipids and to reliably detect lipid biomarkers putatively associated with microbial methane turnover carrying extremely depleted isotopic signatures. This paves the way for a comprehensive exploration of intact lipids associated with microbial methane turnover in environmental samples.
单个脂质的稳定碳同位素组成（δC）在研究碳循环方面具有重要价值。其中，受高甲烷周转率影响的沉积物中的微生物脂质因其独特的贫化同位素指纹而格外突出。然而，气相色谱/同位素比率质谱法（GC/irMS）仅限于挥发性化合物，而完整的极性脂质需要大量预处理，这会导致化学分类信息的丢失。将化合物特异性同位素信息扩展到完整的极性脂质将增强对甲烷微生物周转率的认识。
我们进行了超高效液相色谱/电喷雾电离/高分辨率质谱分析（UHPLC/ESI/HRMS），以分析来自热液甲烷渗漏系统的各种沉积物样品的古菌醇标准品和脂质提取物。使用M1同位素异构体与单同位素异构体M0的比率，我们计算了古菌醇以及各种极性、非气相色谱适用脂质的δC值。将通过比率获得的古菌醇的δC值与通过GC/irMS测量的δC值进行比较。
通过GC/irMS和UHPLC/HRMS方法在天然样品中测定的古菌醇的δC值在很宽的δC值范围内（GC-irMS = -119‰至-34‰）具有很强的相关性（R = 0.94；N = 76 - 82）。与甲烷周转率相关的生物标志物的δC值始终低于-60‰，而可能与基于光合作用的食物网相关的化合物的δC值则保持在-45‰以上。古菌醇标准品的UHPLC/HRMS测量进一步表明，δC值可以在大约一个数量级的M0信号强度范围内可靠地测定。
我们的结果表明，UHPLC/HRMS测量的M1/M0比率可用于评估非气相色谱适用脂质的碳同位素指纹，并可靠地检测可能与携带极度贫化同位素特征的微生物甲烷周转相关的脂质生物标志物。这为全面探索环境样品中与微生物甲烷周转相关的完整脂质铺平了道路。
