25th International Meeting on Organic Geochemistry IMOG 2011

P-433
Environmental occurrence of oxic degradation products of
anammox ladderane lipids
Darci Rush 1 , Andrea Jaeschke 1,2 , Ellen Hopmans 1 , Stuart Wakeham 3 , Stefan Schouten 1 ,
Jaap Sinninghe Damsté 1
1 NIOZ Royal Netherlands Institute for Sea Research, Department of Marine Organic Biogeochemistry, Den
Hoorn, Netherlands, 2 ETH Zürich, Institute of Geochemistry and Petrology, Zurich, Switzerland, 3 Skidaway
Institute of Oceanography, Savannah, United States of America (corresponding author:darci.rush@nioz.nl)
Anaerobic ammonium oxidation (anammox), a
bacterially mediated process in the marine nitrogen
cycle, has been shown to contribute substantially to
the loss of fixed inorganic nitrogen from the ocean
system [1]. Understanding the role of anammox in
different environments is crucial in characterizing the
nitrogen cycle. Ladderane lipid biomarkers are unique
to the bacteria performing anammox and their
presence in modern environmental settings is
indicative of the occurrence of anammox [2].
However, little is known of the importance of
anammox in past nitrogen cycling, as ladderanes are
thermally labile (due to their cyclobutane structure)
and do not preserve well as such in the sediment
record.
Recently, we found that under oxic conditions
ladderane lipids were degraded to short-chain
ladderane degradation products (Fig 1), which were
rigorously identified by 2D-NMR. The most
pronounced production of these short-chained lipids
during the degradation experiments was at 40 °C and
not at higher temperatures. This suggests that the
degradation of ladderane lipids was microbially
mediated, likely through a β-oxidation pathway, in
which the alkyl side chain of the cyclobutane rings is
shortened in a sequence of reactions that removes
two carbon atoms at a time.
Based on these results, we developed a method to
detect two new biomarkers (I-II; Fig. 1) for the oxic
degradation of ladderane lipids in order to trace their
occurrence in ancient sediments. These shortchained
ladderanes were found in sediments under
the major upwelling area off the coast of Peru even
deeper than the original ladderane biomarkers (42
mbsf), suggesting they might be better preserved.
In the Arabian Sea, the degradation biomarkers were
found to be present already in the oxygen minimum
zone of the water column, suggesting that oxidation of
ladderane lipids may already occur at very low
oxygen concentrations. However, they were not
detected in the euxinic water column of the Cariaco
basin suggesting inhibition of the degradation
pathway in the presence of sulfate. In the Arabian
Sea, these ladderane degradation products increased
in abundance relative to original ladderanes with
sediment depth, which indicates that short-chained
ladderanes might prove to be a more useful marker
for past anammox activity. Moreover, the presence of
short-chained ladderanes in past settings may be
indicative of anammox living under oxygen minimum
conditions rather than in euxinic water columns.
Fig. 1. Structures of ladderane lipids derived from
anammox enrichment cultures (1-4) and their
transformation products derived from microbial oxic
degradation (I-III). 1) C18-[5]-ladderane FA, 2) C20-
[5]-ladderane FA, 3) C18-[3]-ladderane FA, 4) C20-
[3]-ladderane FA, I) C14-[5]-ladderane FA, II) C14-[3]ladderane
FA, III) C16-[3]-ladderane FA.
[1] Hamersley, M.R., et al. (2007) Limnol. Oceanogr.
52, 923-933.
[2] Sinninghe Damsté, J.S., et al. (2002) Nature 419,
708-712.
[3] Dutta and Harayama. (2001) Appl. Environ.
Microbiol. 67, 1970-1974.
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