Tetraether archaeal lipids promote long-term survival in extreme conditions

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. The preponderance of tetraether membrane-spanning lipids in many archaeal clades indicates the fitness advantage of unique membranes for archaeal survival. The inability to rationally control the synthesis of tetraether and cyclized tetraether-lipids has limited investigations into how dynamic shifts in lipid composition support archaeal growth and phase transitions. Employing the facile genetic system of the model hyperthermophilic archaeon Thermococcus kodakarensis that naturally synthesizes abundant tetraether lipids, we identified and targeted the genes necessary for tetraether lipid synthesis and derivatization. While impairing tetraether lipid biosynthesis is possible, the lack of specialized lipids dramatically impairs long-term survival, supporting a critical role for dynamic lipidome changes in supporting archaeal life in the extremes. Unique archaeal lipid membrane composition, including membrane-spanning, tetraether lipids, presumably contribute to survival in extreme pH, temperature, and salinity. The biosynthesis of tetraether lipids in the model species Thermococcus kodakarensis promotes survival at high temperatures, and we demonstrate that alternative lipid species are produced when tetraether lipid biosynthesis is compromised.image