HR: 0800h
AN: B21D-0913    [Abstracts]
TI: Use of carbon isotopes to identify and characterize microbial signatures in hydrothermal settings
AU: * Pancost, R D
EM: r.d.pancost@bristol.ac.uk
AF: University of Bristol, School of Chemistry Cantock's Close, Bristol, BS8 1TS United Kingdom
AU: Pressley, S
EM: n/a
AF: University of Bristol, School of Chemistry Cantock's Close, Bristol, BS8 1TS United Kingdom
AU: Coleman, J
EM: Jo.Coleman@bristol.ac.uk
AF: University of Bristol, School of Chemistry Cantock's Close, Bristol, BS8 1TS United Kingdom
AU: Liane, B G
EM: liane@earth.leeds.ac.uk
AF: University of Leeds, Department of Earth Sciences , Leeds, LS2 9JT United Kingdom
AU: Mountain, B W
EM: B.Mountain@gns.cri.nz
AF: Institute of Geological and Nuclear Sciences, Wairakei Research Centre Private Bag 2000, Taupo, xxxx New Zealand
AB: To further explore the diversity of the microorganisms, their adaptations to extreme environmental conditions and their relationship with geothermal sinter formation, we examined the lipids preserved in six sinters of the Taupo Volcanic Zone (TVZ), New Zealand. These sinters contain microbial remains, but the process of mineralisation has rendered them largely unidentifiable. In contrast, lipids, including free fatty acids, 1,2-diacylglycerophospholipids, 1,2-di-O-alkylglycerols, glycerol dialkyl glycerol tetraethers and 1-O-alkylglycerols, are abundant and can be used as chemotaxonomic indicators. However, interpretation of lipid data and microbial signatures can be complicated by 1) allochthonous (pollen, leaves, fungal spores) inputs; 2) the presence of novel lipids or unknown origin; and 3) the production of the same compounds by a range of microorganisms. This is particularly true in hydrothermal settings, where microorganisms will biosynthesize compounds not commonly attributed to Bacteria or Archaea. Compound-specific carbon isotope analyses can help decipher the lipid signature by distinguishing different organic matter sources. For example, in all TVZ sinters, fatty acids with carbon numbers ranging from C$_{22}$ to C$_{32}$ are present; typically these are attributed to higher plants but they could also represent microbial adaptations to high temperatures. Consistent with the former interpretation, in three of four sinters, high-molecular-weight fatty acid carbon isotopic compositions range from -29 to -32 per mil. However, in a fourth sinter, in which fatty acids are most abundant, their carbon isotopic compositions range from -27 to -41 per mil in a pattern indicative of mixing of two different sources, one of which is almost certainly microbial. Carbon isotopic analyses also shed new light on the sources of novel compounds. Present at one hydrothermal site is a novel series of macrocyclic diethers, analogous to macrocyclic archaeol found in M. jannaschii but with a hydrocarbon skeleton consistent with a bacterial origin. These compounds are enriched in $^{13}$C compared to co-occurring compounds, including normal diethers, suggesting that they derive from a different organism and that they utilise a carbon assimilation pathway that does not discriminate strongly against $^{13}$C (e.g. the reverse tricarboxylic acid pathway or the 3-hydroxypropionate pathway). These results, combined with environmental data, provide useful insight into the metabolism of the source organisms and, thus, their phylogeny, guiding future microbial studies of this setting.
DE: 1030 Geochemical cycles (0330)
DE: 1040 Isotopic composition/chemistry
DE: 1045 Low-temperature geochemistry
DE: 1055 Organic geochemistry
DE: 1094 Instruments and techniques
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting