25th International Meeting on Organic Geochemistry IMOG 2011

O-82
Tetraether lipid profiles in cultures and sediments: novel
structures and geochemical significance
Christopher Knappy 1 , Hugh Morgan 2 , Brendan Keely 1
1 University of York, York, United Kingdom, 2 University of Waikato, Hamilton, New Zealand (corresponding
author:brendan.keely@york.ac.uk)
Since the recognition of the presence and
significance of mesophilic archaea throughout the
oceans, numerous studies have included the
measurement of their glycerol dialkyl glycerol
tetraether (GDGT) lipid cores and related structures
to enable reconstruction of features of the
palaeoenvironment (e.g. Schouten et al., 2008).
Such studies have utilised proxies based on GDGT
lipid cores to reveal sea surface water temperature,
atmospheric air temperature and terrestrial input to
marine and lacustrine environments. The
determination of the tetraether lipid core relative
abundances that are crucial to these proxy
measurements has relied on the measurement of
chromatographic peak areas obtained duing
atmospheric pressure chemical ionisation liquid
chromatography mass spectrometric (APCI LC-MS)
analysis of sediment extracts.
The application of tandem mass spectrometry
during APCI-LC/MS represents a straightforward
means to distinguish structurally distinct families of
tetraether lipid cores in which variation exists in the
number of alkyl chains. Thus, the corresponding
trialkyl (GTGT) and monoalkyl (GMGT) structures
can readily be distinguished from each other and
from the GDGT lipids from their product ion spectra
(Knappy et al., 2009).
An additional benefit of the application of tandem
mass spectrometry is demonstrated by this study.
APCI LC-MS/MS analysis reveals a level of
complexity in the tetraether lipid core distributions
that has not previously been recognised. The
distributions in cultures that have been well
described (e.g. Sulfolobus acidocaldarius) are
shown to contain a series of minor components in
which additional methyl groups appear at various
positions within the structures. The differing
positions of attachment suggest differences in the
biological roles and functions of the different
structural types. Extracts of hyperthermophiles
containing both GDGT and GMGT lipids show a
dominance of the latter and reveal changes in the
lipid core distributions with change in the
temperature at which the cultures are grown,
implying functional significance in the lipid
membrane structure.
The high levels of the GMGT lipid cores in a
Crenarchaeote indicates, contrary to the previous
suggestion that these structures may represent
kingdom-specific biomarkers for the Euryarchaeota
(Schouten et al., 2008), that GMGT lipids are more
widespread throughout the Archaea. The
recognition of the wide structural diversity that
exists among tetraether lipids of organisms grown
in culture indicates that considerably more effort is
required to understand the functional and
distributional significance of the lipids and to
optimise the use of their distributions of the lipid
cores in palaeoenvironmental assessment.
The analysis of sediment extracts by APCI LC-
MS/MS shows the distributions of the tetraether
lipid cores to be highly complex and to contain a
large number of novel and remarkable structures
that challenge our understanding of the routes by
which tetraether lipid cores are formed.
Knappy C.S., Chong J.P.J., Keely B.J. (2009).
Journal of the American Society of Mass
Spectrometry. 20, 51-59.
Schouten S, Baas M, Hopmans EC, Damsté JSS
(2008). Organic Geochemistry, 39, 1033-1038
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