Widespread occurrence of structurally diverse tetraether membrane lipids: Evidence for the ubiquitous presence of low-temperature relatives of hyperthermophiles

Isoprenoid glycerol dialkyl glycerol tetraethers (GDGTs) and branched glyce rol dialkyl diethers are main membrane constituents of cultured hyperthermo philic archaea and eubacteria, respectively, and are found in environments with temperatures >60 degreesC. Recently, we developed a new technique for the analysis of intact core tetraether lipids in cell material and sediment s. The application of this technique to recent sediments shows that known a nd newly identified isoprenoid and branched GDGTs are widespread in low-tem perature environments (<20<degrees>C) and are structurally far more diverse than previously thought. Their distribution indicates the ubiquitous envir onmental presence of as yet uncultivated, nonthermophilic organisms that ma y have independently evolved from hyperthermophilic archaea and eubacteria. The structures of some of the new GDGTs point to the hybridization of both typical archaeal and eubacterial biosynthetic pathways in single organisms .