Intact Membrane Lipids of “Candidatus Nitrosopumilus maritimus, ” a Cultivated Representative of the Cosmopolitan Mesophilic

In this study we analyzed the membrane lipid composition of “Candidatus Nitrosopumilus maritimus, ” the only cultivated representative of the cosmopolitan group I crenarchaeota and the only mesophilic isolate of the phylum Crenarchaeota. The core lipids of “Ca. Nitrosopumilus maritimus ” consisted of glycerol dialkyl glycerol tetraethers (GDGTs) with zero to four cyclopentyl moieties. Crenarchaeol, a unique GDGT containing a cyclohexyl moiety in addition to four cyclopentyl moieties, was the most abundant GDGT. This confirms unambiguously that crenarchaeol is synthesized by species belonging to the group I.1a crenarchaeota. Intact polar lipid analysis revealed that the GDGTs have hexose, dihexose, and/or phosphohexose head groups. Similar polar lipids were previously found in deeply buried sediments from the Peru margin, suggesting that they were in part synthesized by group I crenarchaeota. Crenarchaeota, one of the phyla in the domain Archaea, has long been thought to consist mostly of (hyper)thermophiles, as cultivated representatives had optimal growth temperatures of 40°C and isolates were obtained exclusively from extreme environments, such as sulfidic hot springs (reference 28 and references therein). Culture-independent DNA surveys, how