古菌和细菌四醚膜脂GDGTs的生物合成机制及其生物地球化学意义

以甘油二烷基甘油四醚(glycerol dialkyl glycerol tetraethers，GDGTs)为主的跨膜醚脂化合物是古菌和部分细菌细胞膜的重要组成成分。作为分子化石，GDGTs化合物对环境变化响应敏感，以其为基础的有机地球化学指标在定量重建海洋与陆地的古环境研究中发挥出独特的优势。然而，GDGTs指标在广泛应用的同时也不断出现适用性和准确性问题。其关键原因在于GDGTs的生物合成和生理机制研究相对匮乏，难以为指标提供分子生物学与生理学基础。近年来，在多学科的交叉融合下，古菌类异戊二烯GDGTs的生物合成研究取得了令人瞩目的进展。这些成果为脂类生物标志物的地学应用及生物源的确定提供了可靠的生物学基础和新的研究思路。本文综述了古菌类异戊二烯GDGTs的生物合成过程，提出了细菌支链GDGTs生物合成途径的假说，讨论了GDGTs生理过程的生物地球化学意义，并初步展望了GDGTs研究领域未来重要的发展方向。

Biosynthetic pathways of GDGTs in archaea and bacteria and their biogeochemical implications

Glycerol dialkyl glycerol tetraethers (GDGTs) are the main components of membrane-spanning lipids in the cell membranes of archaea and some bacteria. As molecular fossils, GDGTs are sensitive to changes in environmental variables, and GDGT-based proxies have unique advantages in quantitative reconstructions of marine and terrestrial paleoenvironment studies. Although GDGT-based proxies have been widely applied in extensive studies, researchers have increasingly concerned about their fidelity and applicability. The key point lies in the lack of research on the biosynthetic and physiological mechanisms of GDGTs, which results in the deficiency of molecular biological and physiological basis for GDGT-based proxies. Recent breakthroughs achieved with interdisciplinary collaboration in the biosynthesis of archaeal isoprenoid GDGTs provide a reliable biological basis and a new vision for the implication of lipid biomarkers. In this paper, we present a holistic review on the biosynthetic pathway of archaeal isoprenoid GDGTs, propose a hypothetic biosynthetic pathway of bacterial branched GDGTs, and discuss the biogeochemical implications of the physiological process of GDGTs. Finally, we provide an outlook for future research on GDGTs.