Fig. 1.

Structures of diglycerol di(tri)alkyl tetraethers GD(T)GTs commonly synthesized by Archaea and molecular weights shown as m/z values. GDGT-X was recently identified as a major core GDGT in the soil AOA “Ca. Nitrososphaera gargensis”; however, it has not been observed in other cultivated Archaea or environmental GDGT distributions thus far. Below, IPLs identified in this work (and also in “Ca. Nitrosopumilus maritimus” and “Ca. Nitrososphaera gargensis”); polar headgroups are shown in full structure: monohexose (MH), dihexose (DH), phosphohexose (PH), and hexose + phosphohexose (HPH). It should be noted that the exact positions of the polar headgroups are unknown.