FIG. 4.

ESI mass spectra (corrected for background) of (A) tentatively identified crenarchaeol with a hexose head group, (B) tentatively identified GDGT 0 with two hexose moieties as the head group, (C) an unknown polar lipid, (D) tentatively identified crenarchaeol with a phosphoglycerol head group, and (E) tentatively identified crenarchaeol with hexose and phosphoglycerol head groups in a polar lipid extract of “Ca. Nitrosopumilus maritimus.” Note that the positions and structures of the hexose moieties are tentative as the position and structure cannot be established from mass spectral data.