Archaea synthesize heterochiral phospholipid membranes as revealed by chiral analysis of archaeols.

This study comprehensively characterizes structural diversity of archaeol lipids in selected archaeal genera, integrating available genomic information with advanced lipidomic and stereochemical analyzes. Study of genomes from six archaeal genera revealed the presence of key enzymes involved in glycerophosphate biosynthesis, namely glycerol-1-phosphate dehydrogenase and glycerol-3-phosphate dehydrogenase. Their coexistence in some of the studied strains suggests the ability of these organisms to synthesize both enantiomeric forms of glycerol phosphates. Shotgun lipidomic profiling confirmed the presence of saturated and unsaturated archaeols, including extended forms (C20-C25), hydroxyarchaeols, and tetraether lipids, especially in the species Haloferax volcanii, Methanopyrus kandleri, and Sulfolobus acidocaldarius. Using on-line 2D LC-MS/MS, a specific molecular species of archaeol (20:3-25:4-AR) with seven double bonds was identified in H. volcanii, while bis-extended archaeol (C25-C25) was not detected. Chiral HPLC of a commercial archaeol standard resolved four isomers, with the (R)-2,3-di-O-phytanyl-sn-glycerol stereoisomer being the most abundant (> 80 %). In four of our archaeal strains a minor S enantiomer was present at concentrations of 6.8-13.9 % relative to the main R isomer, and its presence coincided with the presence of both glycerol phosphate dehydrogenases in the respective genomes. The distribution of these isomers across the studied strains supports the coexistence of both R- and S- enantiomers of archaeols in some, but not all, archaeal lineages. These findings highlight the stereochemical and structural complexity of archaeal membrane lipids and provide new insights into their biosynthetic diversity.