Novel Extended Tetraether Lipids Found in a High-CO2 Geyser

The growing research into the archaeal lipidome has uncovered a remarkable structural diversity in glycerol dialkyl glycerol tetraethers (GDGTs) and revealed complex membrane adaptations, especially in extreme environments. We performed a comprehensive analysis of the lipidome from the subsurface water of a CO2-rich, cold-water Geyser Andernach (Germany), using ultra-high-resolution mass spectrometry methods. We detected GDGT-0, presumably derived from the dominant community member Candidatus Altiarchaeum, providing evidence for its ability to synthesize tetraethers as previously predicted from metagenomic data. Beyond the typical GDGT-0 and acyclic glycerol trialkyl glycerol tetraether (GTGT-0), we discovered novel structural analogues, here referred to as extended GDGTs and GTGTs, characterized by the asymmetrical addition of up to two isoprenoid units to only one of their hydrocarbon side chains, analogous to those found in extended archaeols. The lack of GDGT ring synthase A (GrsA) and GrsB homologs in the corresponding metagenome-assembled genome, suggests that the producing archaeon may utilize extended GDGTs as a membrane adaptation to cope with the energy-depleted conditions of the geyser environment, highlighting the adaptive flexibility of archaea to extreme physicochemical conditions.