25th International Meeting on Organic Geochemistry IMOG 2011

P-424
Intact polar lipid and associated genetic signatures of archaea in
estuarine sediments
Travis B. Meador 1,2 , Cassandre Lazar 2,3 , Marcos Y. Yoshinaga 1,2 , Andreas Teske 3 , Kai-
Uwe Hinrichs 1,2
1 University of Bremen, Bremen, Germany, 2 MARUM Center for Environmental Sciences, Bremen, Germany,
3 University of North Carolina, Chapel Hill, Chapel Hill, United States of America (corresponding
author:travis.meador@uni-bremen.de)
Members of the Miscellaneous Crenarchaeotal Group
(MCG) appear to have a widespread global
distribution but their metabolic capabilities or
ecological relevance remain uncertain. [1,2] Some
studies have suggested that these crenarchaeota
may be involved in the anaerobic oxidation of
methane. [3,4,5] Recently, the archaeal community in
sediments of the White Oak River Estuary (NC, USA)
was shown to be primarily composed of MCG. [6] We
collected sediment cores from this estuary to further
explore the distribution of MCG by intact polar lipid
(IPL) and genetic signatures, as well as the
geochemical conditions that give rise to their success
in this environment. We targeted sediments with a
distinct sulfate-methane transition zone (SMTZ),
where there may exist a natural enrichment of MCGspecific
IPLs.
Reports of IPL distributions in the natural
environment are limited to a few studies, which have
shown that archaeal diether and tetraether lipids
comprise the bulk of IPLs in subsurface sediments. [7]
However, there was relatively little variability observed
in lipid headgroup distribution compared to the
diversity of microbial assemblages inferred from
analysis of nucleic acids. [8] The most ubiquitous IPL
reported in this study, diglycosyl glycerol dibiphytanyl
glycerol tetraether (2Gly-GDGT), accounted for more
than half of all IPLs from sediment horizons located
within the sulfate-methane transition zone of
sediments collected from the Peru Margin.
In the White Oak River Estuary, we observed a
subsurface sulfate maximum in all cores (up to
16 mM; 10-12 cm), with subsequent depletion
downcore to below detection limits at 30 cm. At this
depth, methane concentrations began to increase,
reaching a maximum at the deepest depth horizons
(~0.5 mM; 50 cm). Within this SMTZ, we detected
2Gly-GDGT in addition to several other archaeal IPLs
(Fig. 1). In particular, we observed relatively higher
abundances of tetraethers with a headgroup of mass
341 Da (H341-GDGT(1); m/z=1656.5 Da) and
phosphatidyl-N-methylethanolamine (PME-GDGT,
m/z =1427.3 Da). These IPLs increase in
concentration within the SMTZ and are likely products
of the active populations of Archaea that inhabit these
estuarine sediments. Further evaluation of the
archaeal communities associated with these IPL
signatures by clone libraries, and pyrosequencing, in
addition to intramolecular and isotopic composition
analysis of these archaeal IPLs will help to unveil the
metabolic activity associated with natural populations
of MCG.
Figure 1. Depth profiles of selected IPLs in estuarine
sediment. Phosphatidylcholine diacylglycerol (PC-DAG; ‚) is
included as reference for bacterial lipid contribution. Relative
abundances of each IPL are expressed as the response of
molecular ions generated during LC-ESI-MS, [9] normalized to
that of an internal extraction standard (C21-PC-DAG). The
grey box represents the depth of the SMTZ.
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5. Inagaki, F., et al. 2006. PNAS 103(8): 2815-2820.
6. Lloyd, K. 2009. Microbially-driven methane and sulfur
cycling in a Gulf of Mexico methane seep and the White
Oak River Estuary. PhD Thesis, U. North Carolina.
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628.
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