Henry A. Boumann

Intact Membrane Lipids of "Candidatus Nitrosopumilus maritimus," a Cultivated Representative of the Cosmopolitan Mesophilic Group I Crenarchaeota

ABSTRACT 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.

The selective utilization of substrates in vivo by the phosphatidylethanolamine and phosphatidylcholine biosynthetic enzymes Ept1p and Cpt1p in yeast

In yeast, the aminoalcohol phosphotransferases Ept1p and Cpt1p catalyze the final steps in the CDP‐ethanolamine and CDP‐choline routes leading to phosphatidylethanolamine (PE) and phosphatidylcholine (PC), respectively. To determine how these enzymes contribute to the molecular species profiles of PE and PC in vivo, wild‐type, cpt1Δ, and ept1Δ cells were pulse labeled with deuterated ethanolamine and choline. Analysis of newly synthesized PE and PC using electrospray ionization tandem mass spectrometry revealed that PE and PC produced by Ept1p and Cpt1p have different species compositions, demonstrating that the enzymes consume distinct sets of diacylglycerol species in vivo. Using the characteristic phospholipid species profiles produced by Ept1p and Cpt1p as molecular fingerprints, it was also shown that in vivo CDP‐monomethylethanolamine is preferentially used as substrate by Ept1p, whereas CDP‐dimethylethanolamine and CDP‐propanolamine are converted by Cpt1p.

The contributions of biosynthesis and acyl chain remodelling to the molecular species profile of phosphatidylcholine in yeast

Phosphatidylcholine (PC) is a very abundant membrane lipid in most eukaryotes, including yeast. The molecular species profile of PC, i.e. the ensemble of PC molecules with acyl chains differing in number of carbon atoms and double bonds, is important for membrane function. Pathways of PC synthesis and turnover maintain PC homoeostasis and determine the molecular species profile of PC. Studies addressing the processes involved in establishing the molecular species composition of PC in yeast using stable isotope labelling combined with detection by MS are reviewed.