Analysis of lipids from a hydrothermal vent methanogen and associated vent sediment by supercritical fluid chromatography

Lipids from a thermophilic methanogen and the associated hydrothermal vent sediment (Guaymas Basin, Gulf of California) were analyzed by gas chrmotography-mass spectrometry (GC-MS) and supercritical fluid chromatography (SFC). The neutral lipids of the thermophilic methagonen consisted of straight chain alkanes (nC₂₂ to nC₃₆), with nC₂₄, nC₂₈, nC₃₂ and nC₃₆ predominating and C₂₅, C₃₀ and C₃₅-isoprenoids and hydroisoprenoids. The squalene (C₃₀) series was the most abundant (95.6%). The backbone structure of the novel C₃₅-isoprenouds was tentatively identified as 2,6,10,14,19,23,27-heptamethyloctacosane. Polar lipids of the thermophilic methanogen were analyzed by SFC and consisted fo diphytanyl glyceril diether (61.6%), macrocyclic glycerol diether (15.3%), dibiphytanyl diglycerol tetraether (11.8%) and an unidentified component (11.4%).Biomarker analysis of the Guaymas Basin sediment revealed the presence of small amounts of polyunsaturated C₃₀-isoprenoids, with a distribution similar to the C₃₀-isoprenoids of the thermophilic methanogen. In addition, the sediment contained ‘free’ diphytanyl glycerol diether as predominant ether lipid. Low levels of polar ether lipids, indicative of ‘active’ archaebacteria, were also detected. Results suggest that Guaymas Basin sediment recently contained active microbial populations with a lipid profile similar to the isolated thermophilic methanogen.