Influence of ammonia oxidation rate on thaumarchaeal lipid composition and the TEX86 temperature proxy

Archaeal membrane lipids known as glycerol dibiphytanyl glycerol tetraethers (GDGTs) are the basis of the TEX86 paleotemperature proxy. Because GDGTs preserved in marine sediments are thought to originate mainly from planktonic, ammonia-oxidizing Thaumarchaeota, the basis of the correlation between...

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Bibliographic Details
Published in:Proceedings of the National Academy of Sciences - PNAS 2016-07, Vol.113 (28), p.7762-7767
Main Authors: Hurley, Sarah J., Elling, Felix J., Könneke, Martin, Buchwald, Carolyn, Wankel, Scott D., Santoro, Alyson E., Lipp, Julius Sebastian, Hinrichs, Kai-Uwe, Pearson, Ann
Format: Article
Language:English
Subjects:
Ammonia
Ammonia - metabolism
Archaea - metabolism
Culture Techniques
Energy Metabolism
Glyceryl Ethers - metabolism
Lipid Metabolism
Lipids
Nitrification
Oceans and Seas
Oxidation
Oxidation-Reduction
Paleontology - methods
Physical Sciences
Sediments
Temperature
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Summary:Archaeal membrane lipids known as glycerol dibiphytanyl glycerol tetraethers (GDGTs) are the basis of the TEX86 paleotemperature proxy. Because GDGTs preserved in marine sediments are thought to originate mainly from planktonic, ammonia-oxidizing Thaumarchaeota, the basis of the correlation between TEX86 and sea surface temperature (SST) remains unresolved: How does TEX86 predict surface temperatures, when maximum thaumarchaeal activity occurs below the surface mixed layer and TEX86 does not covary with in situ growth temperatures? Here we used isothermal studies of the model thaumarchaeon Nitrosopumilus maritimus SCM1 to investigate how GDGT composition changes in response to ammonia oxidation rate. We used continuous culture methods to avoid potential confounding variables that can be associated with experiments in batch cultures. The results show that the ring index scales inversely (R² = 0.82) with ammonia oxidation rate (ϕ), indicating that GDGT cyclization depends on available reducing power. Correspondingly, the TEX86 ratio decreases by an equivalent of 5.4 °C of calculated temperature over a 5.5 fmol·cell−1·d−1 increase in ϕ. This finding reconciles other recent experiments that have identified growth stage and oxygen availability as variables affecting TEX86. Depth profiles from the marine water column show minimum TEX86 values at the depth of maximum nitrification rates, consistent with our chemostat results. Our findings suggest that the TEX86 signal exported from the water column is influenced by the dynamics of ammonia oxidation. Thus, the global TEX86–SST calibration potentially represents a composite of regional correlations based on nutrient dynamics and global correlations based on archaeal community composition and temperature.
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.1518534113