Factors controlling the lipid composition of marine planktonic Thaumarchaeota

Marine ammonia-oxidizing archaea of the phylum Thaumarchaeota synthesize glycerol dibiphytanyl glycerol tetraether (GDGT) membrane lipids that are used as for the reconstruction of sea surface temperatures by means of the TEX86 paleothermometer. Discrepancies between observed and predicted TEX86-temperatures throughout the global ocean indicate that the physiological and ecological controls on lipid composition in planktonic Thaumarchaeota remain poorly understood. In this thesis, the influence of growth phase, temperature, pH, and salinity on the membrane lipid composition of Thaumarchaeota were investigated. The results indicate that TEX86 is not only influenced by temperature but similarly by growth phase and community composition, which compromises its utility as a paleothermometer. A comprehensive study of the lipidomes of 11 thaumarchaeal cultures revealed that Thaumarchaeota contain a high diversity of membrane lipids that is related to phylogeny as well as growth characteristics. This analysis further revealed that all Thaumarchaeota contain the specific biomarkers crenarchaeol, methoxy archaeol, and saturated menaquinone-6