25th International Meeting on Organic Geochemistry IMOG 2011

O-13
Degradation of intact polar lipids in sandy sediments: Insights
from a laboratory experiment
Jörn Logemann, Jutta Graue, Jürgen Köster, Bert Engelen, Heribert Cypionka, Jürgen
Rullkötter
University of Oldenburg, Oldenburg, Germany (corresponding author:j.logemann@icbm.de)
Intact polar lipids (IPLs) occur in the cytoplasm
membranes of all living organisms and are therefore
commonly used as biomarkers for living biomass
[1-5]. Also, IPLs are employed as chemotaxonomic
markers to distinguish living bacterial from living
archaeal cells [1, 6]. The analytical distinction of
microorganisms is possible due to the unique feature
of Archaea synthesizing IPLs containing ether-bound
isopreniod core lipid structures. In contrast, bacterial
and eukaryal cytoplasma membranes contain mainly
intact polar lipids with unbranched ester-bound
straight-chain fatty acid core lipids.
One fundamental assumption underlies these
applications: Intact polar lipids are considered to
degrade rapidly after cell death [7]. The lack of a
broad study on the degradation of intact polar lipids,
which encloses lipids with phosphoester and
glycosidically bound head groups and moieties that
occur in Bacteria and Archaea made it necessary to
revisit the degradation of IPLs to ensure the
robustness of this proxy.
The turnover of IPLs was investigated in a laboratory
experiment with anoxic sandy sediments from the
North Sea. As IPL sources intact cells of two
organisms that do not naturally occur in North Sea
sediments were chosen: (i) Saccharomyces
cerevisiae as the source of ester-bound acyl lipids
that also occur in bacteria, and (ii) the hypersaline
archaeon Haloferax volcanii as the source of etherbound
isoprenoid lipids. The degradation of these two
types of IPLs was monitored and concurrent changes
in the microbial community in the course of the
experiment were tracked. Pore water and 16S rRNAbased
DGGE analysis helped to gain background
information on processes occurring during the
experiment. The results of the degradation
experiment were tested with two controls: The first
control (named: ―abiotic control‖) was designed to
assess if any processes occur which lead to a
degradation of the added intact polar lipids but are not
mediated by microorganisms. The second control
(named: ―untreated control‖) was used to check the
influence of the addition of inactive biomass on the
microbial community without any further substrate
addition. Although a notable amount of IPL source
material was added, the obtained data showed only a
minor influence on microbial metabolism and
community profile.
Peak area ratio relative to day 0
2.0
1.5
1.0
0.5
Ester
Ether
0.0
0 20 40 60
Time [d]
80 100
Figure 1: Sum of ester- and ether-bound IPLs in the
degradation experiment and the abiotic control given in peak
area ratios relative to day 0. Closed symbols: degradation
experiment; open symbols: abiotic control. For creation of
plots for the abiotic control the same IPLs were chosen as
for the plots of the degradation experiment.
The results show relatively fast degradation of esterbound
IPLs and no significant degradation of archaeal
ether-bound IPLs. Thus, this differential degradation
of IPLs may lead to bias in the sedimentary record
and perhaps to an overestimation of active archaeal
communities.
[1] Biddle et al. (2006) PNAS 103, 3846-3851.
[2] Ertefai et al. (2008) Org. Geochem 39, 1572-1588.
[3] Rossel et al. (2008) Org. Geochem 39, 992-999.
[4] Sturt et al. (2004) RCM 18, 617-628.
[5] Zink et al.(2003) Org. Geochem. 34, 755-769.
[6] Lipp et al. (2008) Nature 454, 991-994.
[7] Harvey et al. (1986), GCA 50, 795-804.
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