The tail-to-tail linked C40 isoprenoid hydrocarbon lycopane is a biomarker found in a wide variety of environments and in some extremophilic archaea but is also a possibly degradation product of a carotenoid (bacterioruberin) as well as plants (various lycopenes) and green algae (lycopadiene). Although potential producers are known, the source of lycopane in water-column and sedimentary environments is commonly ambiguous. In this study, the occurrence of 13C-depleted lycopane (δ13C = −114 to −106 ‰) in authigenic, sulfur-bearing carbonates from Monte Palco (Sicily) is used to re-evaluate the environmental significance of lycopane. In the Monte Palco authigenic carbonates, lycopane is accompanied by other, similarly 13C-depleted apolar isoprenoids such as PMI, squalane, and sulfurized homologues, including a tail-to-tail linked C35 isoprenoid, as well as typical lipids of anaerobic methanotrophic archaea (ANME) like glycerol dibiphytanyl glycerol tetraether (GDGT)-0, −2, archaeol, and sn3-hydroxyarchaeol. The δ13C values of lycopane reveal linear correlations with values of PMI and squalane (n = 7; r2 = 0.71 and 0.82, respectively), probably reflecting a similar cellular function of the tail-to-tail linked isoprenoids in the archaeal source organisms. Lycopane is interpreted to represent a membrane intercalant, produced in response to extreme environmental conditions. The new observations resulting from the analysis of the Monte Palco authigenic carbonates – including the similarities in 13C-depletion of PMI, squalane, and lycopane but also with other archaeal membrane lipids like archaeol, sn3-hydroxyarchaeol, and GDGT-0 (measured as ether-cleaved biphytanes) – allowed us to re-interpret the potential source organism of lycopane in modern and ancient anoxic and euxinic basins (Cariaco Trench, Black Sea, late Cenomanian black shales of the Cape Verde Basin). These new data agree with unknown archaea as producers of lycopane as a response to environmental stress at chemoclines. The previous interpretation of lycopane as a biomarker of photoautotrophic bacteria in anoxic basins is challenged by our new findings. An alternative explanation for these occurrences is lycopane production by Marine Group II Euryarchaeota, archaea closely associated with primary producers. Lycopane production by archaea is probably more widespread than previously recognized. Future research should evaluate the potential of lycopane as a biomarker of archaeal adaptation to extreme environmental conditions.

中文翻译：

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基于番茄烷在自生含硫碳酸盐中的存在重新解释番茄烷作为古细菌的生物标志物


尾对尾连接的 C40 类异戊二烯烃番茄烷是在多种环境和一些极端古细菌中发现的生物标志物，但也可能是类胡萝卜素（细菌红素）以及植物（各种番茄红素）和绿藻的降解产物（番茄二烯）。尽管潜在的生产者是已知的，但水柱和沉积环境中番茄烷的来源通常是模糊的。在本研究中，利用来自 Monte Palco（西西里岛）的自生含硫碳酸盐中 13C 贫化的番茄烷（δ13C = -114 至 -106 ‰）的存在来重新评估番茄烷的环境意义。在 Monte Palco 自生碳酸盐中，番茄烷伴随着其他类似的 13C 耗尽的非极性类异戊二烯，例如 PMI、角鲨烷和硫化同系物，包括尾对尾连接的 C35 类异戊二烯，以及厌氧甲烷氧化古细菌的典型脂质。 ANME）如甘油二联植烷基甘油四醚（GDGT）-0、-2、古菌醇和 sn3-羟基古菌醇。番茄烷的 δ13C 值揭示了与 PMI 和角鲨烷值的线性相关性（n = 7；r2 = 0.71 和 0.82，分别），可能反映了古菌源生物中尾对尾连接的类异戊二烯的类似细胞功能。番茄烷被解释为代表一种膜嵌入剂，是针对极端环境条件而产生的。 对 Monte Palco 自生碳酸盐进行分析得出的新观察结果，包括 PMI、角鲨烷和番茄烷的 13C 消耗的相似性，以及与其他古菌膜脂质如古菌醇、sn3-羟基古菌醇和 GDGT-0（以乙醚测量）的相似性-裂解双植烷）——使我们能够重新解释现代和古代缺氧和低氧盆地（卡里亚科海沟、黑海、佛得角盆地塞诺曼晚期黑色页岩）中番茄烷的潜在来源生物。这些新数据与未知的古细菌一致，它们是番茄烷的生产者，是对趋化素环境压力的反应。我们的新发现挑战了之前对番茄烷作为缺氧盆地光合自养细菌生物标志物的解释。对这些现象的另一种解释是海洋第二类广古菌（与初级生产者密切相关的古菌）产生番茄烷。古细菌生产番茄烷的范围可能比之前认识的更为广泛。未来的研究应该评估番茄烷作为古菌适应极端环境条件的生物标志物的潜力。