(Figure 4) Stable carbon isotopic values and relative contents of biphytanes and sugars from sediment sample from the Peru margin and from the Pakistan margin@en

Glycolipids are prominent constituents in the membranes of cells from all domains of life. For example, diglycosyl-glycerol dibiphytanyl glycerol tetraethers (2Gly-GDGTs) are associated with methanotrophic ANME-1 archaea and heterotrophic benthic archaea, two archaeal groups of global biogeochemical importance. The hydrophobic biphytane moieties of 2Gly-GDGTs from these two uncultivated archaeal groups exhibit distinct carbon isotopic compositions. To explore whether the isotopic compositions of the sugar headgroups provide additional information on the metabolism of their producers, we developed a procedure to analyze the d13C values of glycosidic headgroups. Successful determination was achieved by (1) monitoring the contamination from free sugars during lipid extraction and preparation, (2) optimizing the hydrolytic conditions for glycolipids, and (3) derivatizing the resulting sugars into aldononitrile acetate derivatives, which are stable enough to withstand a subsequent column purification step. First results of d13C values of sugars cleaved from 2Gly-GDGTs in two marine sediment samples, one containing predominantly ANME-1 archaea and the other benthic archaea, were obtained and compared with the d13C values of the corresponding biphytanes. In both samples the dominant sugar headgroups were enriched in 13C relative to the corresponding major biphytane. This 13C enrichment was significantly larger in the putative major glycolipids from ANME-1 archaea (~15 per mil) than in those from benthic archaea (<7 per mil). This method opens a new analytical window for the examination of carbon isotopic relationships between sugars and lipids in uncultivated organisms.糖脂（Glycolipids）是所有生命域细胞膜的重要组成成分。例如，双糖基-甘油二植烷甘油四醚（diglycosyl-glycerol dibiphytanyl glycerol tetraethers，缩写2Gly-GDGTs）与甲烷营养型ANME-1古菌和异养底栖古菌相关，这两类古菌均具有全球生物地球化学重要性。这两类未培养古菌所产生的2Gly-GDGTs的疏水植烷基团展现出截然不同的碳同位素组成。为探究糖头部基团的同位素组成能否为其宿主的代谢途径提供额外信息，我们开发了一种分析糖苷头部基团碳13同位素比值（d13C）的方法。该方法通过以下步骤实现了准确测定：（1）监测脂质提取与制备过程中游离糖带来的污染；（2）优化糖脂的水解条件；（3）将水解得到的糖衍生化为醛糖腈乙酸酯衍生物，该衍生物稳定性足够强，可承受后续的柱纯化步骤。我们获取了两份海洋沉积物样品中从2Gly-GDGTs上裂解得到的糖的d13C初步结果：其中一份样品以ANME-1古菌为主，另一份以底栖古菌为主，并将其与对应植烷基团的d13C值进行了对比。在两份样品中，优势糖头部基团均较对应的主要植烷基团发生了13C富集。ANME-1古菌推定主要糖脂的13C富集程度（约15‰）显著高于底栖古菌的糖脂（<7‰）。该方法为研究未培养生物体内糖与脂质之间的碳同位素关系开辟了全新的分析途径。