25th International Meeting on Organic Geochemistry IMOG 2011

P-418
Extreme intra- and intermolecular carbon isotopic disparity in
individual archaeal intact polar lipids from methane seep
sediments
Marcos Yukio Yoshinaga, Marcus Elvert, Yu-Shih Lin, Kai-Uwe Hinrichs
MARUM, University of Bremen, Bremen, Germany (corresponding author:marcosyukio@gmail.com)
Large carbon isotopic heterogeneity has been
observed in specific lipids and individual cells of
archaeal anaerobic methanotrophs (ANMEs) [1,2,3].
To examine this isotopic variability in detail, we
studied the carbon isotopic compositions of archaeal
intact polar lipids (IPLs) and sedimentary carbon
pools (TOC, lactate, acetate, methane, dissolved
inorganic carbon) in a push corer (0-14 cm) from a
methane seep off Pakistan. After preparative liquid
chromatography (LC) separation, individual IPLs were
subjected to ether cleavage and reduction, followed
by isotopic ratio analysis of the resulting phytane and
biphytanes derivatives as well as of sugar
headgroups that were obtained from glycosidic (Gly)
IPLs after hydrolytic cleavage [4]. This IPL-specific
isotopic analysis is expected to strongly reduce
effects related to mixing of lipid pools from different
sources and is more likely to resolve the true diversity
of carbon metabolisms within complex microbial
communities.
Isotopic offsets of up to 80‰ were observed
between core lipids and related hexoses within 2Glyglyceroldialkylglyceroltetraether
(2Gly-GDGT, Fig. 1),
one of the most common archaeal IPLs in marine
sediments. A large isotopic difference is as well
evident between biphytanes from 2Gly-GDGT and
other archaeal IPLs, i.e. glycerolphosphate (PG)-
GDGTs. The data can be divided in two clusters: (1)
higher 13 C-depletion than methane; (2) close to or
more positive than � 13 C-TOC. The latter values are
low compared to typical marine sediments, but
comparable to the � 13 C of lactate, suggesting partial
contribution of methane-related organic carbon via
fermentation. Because a considerable fraction of � 13 C
values from sugars and lipids fall into the range of
TOC and lactate, heterotrophy appears to be an
important archaeal metabolism, which is especially
observed in surface sediments and diminishes with
depth. Low �� 13 C values for acetate throughout the
sediment column exclude acetoclastic
methanogenesis as a relevant archaeal metabolism.
The lowest � 13 C values of IPL-derived compounds
result from methane and/or CO2 assimilation by
ANMEs [5]. We estimated the probable � 13 C signature
of CO2 uptake [cf. 6] (gray rectangle in Fig. 1), giving
a � 13 C range lower than IPL derivatives in surface
sediments and one being higher in deeper horizons.
Our results suggest that the diversity of archaeal
metabolic traits in seep sediments is diverse and
responsible for the extreme intra- and intermolecular
� 13 C disparity found in IPLs and prominent carbon
pools.
Figure 1. � 13 C values (‰) of archaeal IPLs derivatives and
carbon metabolites at the 2-3 cm horizon. Gray areas
represent the expected � 13 C range for lipids and biomass of
a methanogen assimilating CO2 [6]. Biphytanes with (0) to
(3) rings. Gal = galactose, Glc = glucose, Man = mannose.
References
[1] Hinrichs, K.-U. et al. (2000) Org Geochem 31: 1685-
1701.
[2] Orphan, V. et al. (2002) PNAS 99: 7663-7668.
[3] House et al. (2009) Environ Microbiol 11: 2207-2215.
[4] Lin, Y.-S. et al. (2010) Rapid Comm Mass Spec 24: 2817-
2826.
[5] Wegener et al. (2008) Environ Microbiol 10: 2287-2298.
[6] Alperin, M.J. and Hoehler, T.M. (2009) Am J Sci 309:
958-984.
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