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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根据石松烷在自生含硫碳酸盐中的出现情况重新解释石松烷作为古细菌的生物标志物


尾对尾连接的 C40 类异戊二烯烃石松烷是一种生物标志物，存在于各种环境和一些极端嗜酸的古细菌中，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（番茄二烯）的降解产物。尽管已知的潜在生产者，但水柱和沉积环境中石松烷的来源通常不明确。在这项研究中，在蒙特帕尔科（西西里岛）的自生含硫碳酸盐中出现的 13C 耗尽石松烷（δ13C = -114 至 -106 ‰）被用来重新评估石松烷的环境意义。在 Monte Palco 自生碳酸盐中，石松烷伴随着其他类似的 13C 耗尽的非极性异戊二烯类化合物，如 PMI、角鲨烷和硫化同系物，包括尾对尾连接的 C35 异戊二烯类，以及厌氧甲烷营养古细菌 （ANME） 的典型脂质，如甘油二双植物基甘油四醚 （GDGT）-0、-2、古细菌和 sn3-羟基古细菌。石松烷的 δ13C 值与 PMI 和角鲨烷的值呈线性相关性（分别为 n = 7;r2 = 0.71 和 0.82），可能反映了古细菌源生物中尾对尾连接的异戊二烯类化合物的相似细胞功能。Lycopane 被解释为代表一种膜嵌入剂，为响应极端环境条件而产生。 对 Monte Palco 自生碳酸盐的分析得出的新观察结果——包括 PMI、角鲨烷和石松烷的 13C 消耗的相似性，以及与其他古细菌膜脂质如古细菌、sn3-羟基古细菌和 GDGT-0（以醚裂解的双植物烷测量）的相似性——使我们能够重新解释现代和古代缺氧和真酸盆地中石松烷的潜在来源生物（Cariaco Trench， 黑海，佛得角盆地的晚 Cenomani 黑色页岩）。这些新数据与未知古细菌一致，作为石松烷的产生者，作为化学还原处对环境压力的响应。先前将石松板解释为缺氧盆地中光合自养细菌的生物标志物，我们的新发现对这一解释提出了挑战。对这些事件的另一种解释是 Marine Group II Euryarchaeota 生产的石松烷，这是一种与初级生产者密切相关的古细菌。古细菌产生的石松烷可能比以前认识到的更广泛。未来的研究应评估石松作为古细菌适应极端环境条件的生物标志物的潜力。