Zhu Chun, Yoshinaga Marcos Y, Peters Carl A, Liu Xiao-Lei, Elvert Marcus, Hinrichs Kai-Uwe
MARUM Center for Marine Environmental Sciences and Department of Geosciences, University of Bremen, D-28359, Bremen, Germany.
Rapid Commun Mass Spectrom. 2014 May 30;28(10):1144-52. doi: 10.1002/rcm.6887.
Studies of archaeal glycerol dibiphytanyl glycerol tetraethers (GDGTs) in the environment and cultures have exclusively focused on compounds with fully saturated alkyl moieties. Here we report a number of novel unsaturated GDGTs (uns-GDGTs) whose alkyl chains contain up to six double bonds and zero to two cyclopentyl moieties.
The identification of these lipids was achieved via comparison of lipid distribution before and after hydrogenation, characteristic retention time patterns, and diagnostic ions using liquid chromatography/tandem mass spectrometry (LC/MS/MS), and ether cleavage products using gas chromatography/mass spectrometry (GC/MS). Isomerism resulting from different unsaturation patterns in the alkyl moieties was observed and specific positions of double bonds in the biphytene and biphytadiene moieties were tentatively assigned.
Uns-GDGTs were detected in sediment and microbial mat samples as both core lipids (CLs) and intact polar lipids (IPLs) associated with mono- or diglycosyl or phosphatidylglycerol headgroups. However, these lipids were overlooked in past investigations because conventional methods for archaeal lipid analysis are unsuitable for uns-GDGTs. Samples from distinct marine environments (Black Sea, Cariaco Basin, Discovery Basin, Eastern Mediterranean Sea, upwelling area off NW Africa, and seep sites off Crimea and Pakistan) were screened for uns-GDGTs using a new LC/MS protocol. The results show that uns-GDGTs contribute significantly to the archaeal lipid pool in anoxic methane-rich environments (Black Sea, Cariaco Basin, and both seep sites) but they were barely detected in the oxic or hypersaline settings.
The characteristic distribution of uns-GDGTs implies that they are attractive targets for future studies aiming at the chemotaxonomy of uncultivated archaea and regulation of uns-GDGT biosynthesis.
对环境和培养物中古菌甘油二植烷甘油四醚（GDGTs）的研究一直仅关注具有完全饱和烷基部分的化合物。在此，我们报告了一些新型不饱和GDGTs（uns-GDGTs），其烷基链含有多达六个双键和零至两个环戊基部分。
通过比较氢化前后的脂质分布、特征保留时间模式以及使用液相色谱/串联质谱（LC/MS/MS）的诊断离子，以及使用气相色谱/质谱（GC/MS）的醚裂解产物，实现了这些脂质的鉴定。观察到由烷基部分不同不饱和模式导致的异构现象，并初步确定了联植烷和双植二烯部分双键的特定位置。
在沉积物和微生物垫样品中检测到uns-GDGTs，它们作为与单糖基或二糖基或磷脂酰甘油头部基团相关的核心脂质（CLs）和完整极性脂质（IPLs）。然而，这些脂质在过去的研究中被忽视了，因为传统的古菌脂质分析方法不适用于uns-GDGTs。使用新的LC/MS方案对来自不同海洋环境（黑海、卡里亚科盆地、发现盆地、东地中海、非洲西北部上升流区以及克里米亚和巴基斯坦近海的渗漏点）的样品进行了uns-GDGTs筛选。结果表明，uns-GDGTs在富含甲烷的缺氧环境（黑海、卡里亚科盆地以及两个渗漏点）中对古菌脂质库有显著贡献，但在有氧或高盐环境中几乎未被检测到。
uns-GDGTs的特征分布表明，它们是未来旨在对未培养古菌进行化学分类和调控uns-GDGT生物合成研究的有吸引力的目标。
