Loki pipe
Archaeal diversity of Loki’s Castle black smokers at the Arctic Mid-Ocean Ridge
16S rRNA gene amplicon study compared to lipid analysis
Hydrothermal vent systems harbor rich microbial communities ranging from aerobic  mesophiles to anaerobic hyperthermophiles. Among these, members of the archaeal domain  dominate the microbial communities in such extreme environments, partly because of their  temperature- and mechanically-resistant membrane lipids. In this study, we use geochemical  and molecular microbiological methods to investigate the abundance and diversity of archaea  in black smoker chimneys from the newly discovered Loki’s Castle hydrothermal vent field  on the Arctic Mid-Ocean Ridge (AMOR) with vent fluid temperatures of 317°C and pH of  5.5. Archaeal glycerol dialkyl glycerol tetraether lipids (GDGTs) with 0 to 4 cyclopentane  moieties were dominant in all sulfide samples and are most likely derived from both  (hyper)thermophilic Euryarchaeota and Crenarchaeota, which are presumably involved in  sulfur and iron reduction, as well as methanogenesis. GDGTs with an additional covalent  bond between the isoprenoid hydrocarbon chains, so-called H-shaped GDGTs and also  containing 0 to 4 cyclopentane rings, were present with similar abundances. These lipids are  not often reported, but may be derived from sulfur-reducing members of the  Thermococcaceae. Crenarchaeol has been detected in samples derived from the chimney  exterior indicating the presence of Thaumarchaeota, involved in ammonia-oxidation (AOA)  at lower ambient temperatures. Our observations based on 16S rDNA-based taxonomy and  biomarker lipid analysis provide insight into microbial communities thriving within the  porous sulfide structures of an active deep-sea hydrothermal vent, where microbial cycling of  sulfur, hydrogen and methane predominantly by archaea may be the prevailing  biogeochemical processes.