The sole unifying feature of the incredibly diverse Archaea is their isoprenoid-based ether-linked lipid membranes. Unique lipid membrane composition, including an abundance of membrane-spanning tetraether lipids, impart resistance to extreme conditions. Many questions remain, however, regarding the synthesis and modification of tetraether lipids and how dynamic changes to archaeal lipid membrane composition support hyperthermophily. Tetraether membranes, termed glycerol dibiphytanyl glycerol tetraethers (GDGTs), are generated by tetraether synthase (Tes) by joining the tails of two bilayer lipids known as archaeol. GDGTs are often further specialized through the addition of cyclopentane rings by GDGT ring synthase (Grs). A positive correlation between relative GDGT abundance and entry into stationary phase growth has been observed, but the physiological impact of inhibiting GDGT synthesis has not previously been reported. Here, we demonstrate that the model hyperthermophile Thermococcus kodakarensis remains viable when Tes (TK2145) or Grs (TK0167) are deleted, permitting phenotypic and lipid analyses at different temperatures. The absence of cyclopentane rings in GDGTs does not impact growth in T. kodakarensis, but an overabundance of rings due to ectopic Grs expression is highly fitness negative at supra-optimal temperatures. In contrast, deletion of Tes resulted in the loss of all GDGTs, cyclization of archaeol, and loss of viability upon transition to the stationary phase in this model archaea. These results demonstrate the critical roles of highly specialized, dynamic, isoprenoid-based lipid membranes for archaeal survival at high temperatures.

中文翻译：

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四醚古菌脂质促进极端条件下的长期生存

极其多样化的古细菌的唯一统一特征是它们的基于类异戊二烯的醚连接的脂质膜。独特的脂质膜成分，包括丰富的跨膜四醚脂质，赋予对极端条件的抵抗力。然而，关于四醚脂质的合成和修饰以及古细菌脂质膜成分的动态变化如何支持高温，仍然存在许多问题。四醚膜，称为甘油二联植烷基甘油四醚 (GDGT)，是由四醚合酶 (Tes) 通过连接两个称为古醇的双层脂质的尾部而产生的。 GDGT 通常通过 GDGT 环合酶 (Grs) 添加环戊烷环来进一步特化。已观察到相对 GDGT 丰度与进入稳定期生长之间呈正相关，但抑制 GDGT 合成的生理影响此前尚未报道。在这里，我们证明，当 Tes (TK2145) 或 Grs (TK0167) 被删除时，模型超嗜热菌Thermococcus kodakarensis仍然存活，从而允许在不同温度下进行表型和脂质分析。 GDGT 中环戊烷环的缺失不会影响T. kodakarensis的生长，但由于异位 Grs 表达而导致环戊烷环过多，在超最佳温度下会产生高度适应性负面影响。相比之下，Tes 的缺失导致所有 GDGT 的丢失、古细菌的环化以及该模型古细菌在过渡到稳定期时活力的丧失。这些结果证明了高度专业化、动态、类异戊二烯脂质膜对于古菌在高温下生存的关键作用。