Intact polar lipid and core lipid inventory of the hydrothermal vent methanogens Methanocaldococcus villosus and Methanothermococcus okinawensis

Abstract For the first time, a comprehensive documentation of the core and intact polar lipid composition of the hydrogenotrophic, (hyper)thermophilic, methanogenic archaea Methanocaldococcus villosus strain DSM 22612 T and Methanothermococcus okinawensis strain DSM 14208 T is provided. Intact polar lipids of both organisms consist almost exclusively of glycolipids. M. villosus has mainly diglycosidic and some monoglycosidic head groups. In contrast, M. okinawensis is typified by more monoglycosidic than diglycosidic head groups and some phosphoglycosidic head groups. Both strains exhibit mainly diether lipids, namely archaeol and macrocyclic archaeol, which together account for 95% of the total core lipids. M. villosus reveals more macrocyclic archaeol (55%) than archaeol (39%). In M. okinawensis the ratio is almost reversed (35% macrocyclic archaeol; 59% archaeol). Both organisms also show minor relative abundances of GDD-0 (glycerol dialkyl diether) and GMD-0 (glycerol monoalkyl diether). The two methanogens also contained minute abundances of tetraether lipids. GDGT-0 (glycerol dialkyl glycerol tetraether) was dominant and accompanied by smaller amounts of GMGT-0 (glycerol monoalkyl glycerol tetraether) and GTGT-0 (glycerol trialkyl glycerol tetraether). Two isomers of GMGT-0 occurred in both organisms, whereas one was predominant in M. villosus and the other one in M. okinawensis . The detection of macrocyclic archaeol represents the first report of this compound in the genus Methanothermococcus . GTGT-0 and GMGT-0 have so far not been described in any representative of both genera, and two isomers of GMGT-0 not in any other organism. These new observations will be instrumental for the interpretation of archaeal-derived molecular fossils in environmental samples.