Stable hydrogen isotope fractionation in archaeal glycerol tetraether lipids is largely independent from metabolism and culture conditions
Abstract
The stable H isotope composition of persistent biomolecules is often used as a hydrological proxy for paleoenvironmental studies. While most previous work has focused on leaf wax-derived n-alkanes, the potential of microbial lipid biomarkers as carriers of H isotope signatures is underexplored. We therefore investigated the H isotope fractionation between the membrane lipids of cultured Archaea and ambient water in three taxa, and assessed the stable H isotope composition of their glycerol-tetraether membrane lipids by ether cleavage and GC-Pyrolysis-IRMS analysis of the biphytanyl chains. In contrast to recent work on bacterial fatty acids, where the direction and magnitude of fractionation was highly variable (up to 600 ‰) and largely depended on metabolic substrate and pathways of energy metabolism, our data show fairly consistent 2H fractionation between lipids and growth water within a range of -180 to -270 ‰ V-SMOW, across three metabolically diverse Archaea: The ammonium-oxidizing chemoautotroph Nitrosopumilus maritimus (Thaumarchaeota), the versatile chemoautotroph Acidianus sp. DS80, and the thermo-acidophilic heterotroph Sulfolobus acidocaldarius (both Crenarchaeota). Culture conditions varied from 28 to 80 °C, pH 2.0 to 7.6, and electron donors included NH3 (N. maritimus), H2 (DS80) , S0 (DS80), and sucrose (S. acidocaldarius). The surprisingly narrow range of 2H fractionation factors observed suggests these lipids have potential as paleo-hydrological proxies, either in addition or as an alternative to leaf wax n-alkanes. Moreover, the extent of 2H fractionation between water and the biphytanyl chain seems to vary systematically within a range of ∼10 ‰ depending on the number of rings (cyclopentyl + cyclohexyl), with distinct patterns between experiments and conditions. We argue that these differences in 2H content are related to saturation and concomitant cyclization of the biphytanyl chains, and can give important clues on the yet unresolved details of tetraether biosynthesis.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.B51C..01P
- Keywords:
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- 0424 Biosignatures and proxies;
- BIOGEOSCIENCES;
- 0473 Paleoclimatology and paleoceanography;
- BIOGEOSCIENCES;
- 4912 Biogeochemical cycles;
- processes;
- and modeling;
- PALEOCEANOGRAPHY;
- 4924 Geochemical tracers;
- PALEOCEANOGRAPHY