HR: 1330h
AN: B12A-0773    [PDF]
TI: Geolipids produced by methanogens and sulfate-reducing bacteria at the Lost City Hydrothermal Field
AU: * Bradley, A S
EM: bradleya@mit.edu
AF: Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 77 Massachusetts Ave., Cambridge, MA 02139 United States
AU: Hayes, J M
EM: jhayes@whoi.edu
AF: Woods Hole Oceanographic Institution, Department of Geology and Geophysics, 266 Woods Hole Road, Woods Hole, MA 02543 United States
AU: Summons, R E
EM: rsummons@mit.edu
AF: Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 77 Massachusetts Ave., Cambridge, MA 02139 United States
AB: Molecular biomarkers document the presence in a geologic system of particular microbial lineages, or of microbes that use specific metabolic processes. Lipid extracts from carbonate rocks of the Lost City Hydrothermal Field yield a predominance of biomarkers diagnostic for methanogenic archaea including the ether lipids archaeol, {\it sn}-2 and {\it sn}-3 hydroxyarchaeol, and dihydroxyarchaeol and the hydrocarbon 2,6,10,15,19-pentamethylicosane (PMI). Sterols and hopanoids, diagnostic for eukaryotes and bacteria respectively, were subordinate. At ten sites surveyed thus far, biomarker types were not correlated with vent temperature or activity. Hydroxyarchaeols were detected in three active (T $\geq$ $70\deg$C) and two inactive vents. Glycerol monoethers with saturated and unsaturated C15-C20 n-alkyl chains, diagnostic for sulfate-reducing bacteria, were detected in five active and three inactive vents. Carbohydrates were detected in four active vents, but not in the inactive vents. High concentrations of {\it sn}-2 and {\it sn}-3 hydroxyarchaeol and a dihydroxyarchaeol at a $70\deg$C site (sample 3869-1404) suggest that methane cycling is the dominant metabolic processes at this location. The presence of methanogens at this site is confirmed by the presence of pentamethylicosane. Stable isotopic compositions of these biomarkers will be used to determine whether these methanogens are consuming or producing methane. This sample also contains C16 and C18 saturated glycerol monoethers. In conjunction with genomic studies, the biomarker analyses will document the metabolic roles of microbes in this system.
DE: 0400 Biogeosciences
DE: 1050 Marine geochemistry (4835, 4850)
DE: 1055 Organic geochemistry
SC: Biogeosciences [B]
MN: 2003 Fall Meeting