25th International Meeting on Organic Geochemistry IMOG 2011

O-44
Bacterial formation of (di)ether lipids: a state of the art
Vincent Grossi 1 , Agnès Hirschler-Réa 2 , Philippe Schaeffer 3 , Cristiana Cravo-Laureau 4
1 CNRS - Université de Lyon, Villeurbanne, France, 2 IRD, Universités de Provence et de la Méditerranée,
Marseille, France, 3 CNRS - Université de Strasbourg, Strasbourg, France, 4 Université de Pau et des Pays
de l’Adour, Pau, France (corresponding author:vincent.grossi@univ-lyon1.fr)
The actual knowledge of the biosynthesis of
glycerol ether lipids by Bacteria will be reviewed and
expanded with recent results showing for the first time
the production of dialkyl glycerol diethers (DGDs) by a
mesophilic (hydrocarbon-degrading) marine sulfatereducing
bacterium (SRB).
One of the distinguishing features between Archaea
and Bacteria is the chemical composition of their
cellular membranes. Bacteria generally synthesise
phospholipids (non-isoprenoid alkyl chains esterified
to glycerol) whereas archaeal membrane lipids are
composed of isoprenoid di- and tetraethers of glycerol
(isoprenoid DGDs and GDGTs, respectively). These
different chemical structures have implication in term
of ecology and evolution, and are frequently used to
distinguish between Bacteria and Archaea in
(paleo)environmental studies. Non-isoprenoid DGDs
and GDGTs constitute an exception to these chemical
distinctions as they exhibit an intriguing combination
of structural characteristics of Bacteria and Archaea.
Non-isoprenoid DGDs are relatively uncommon in
bacteria but have been reported in some
(hyper)thermophilic bacteria, planctomycetes and
myxobacteria [1]. However, these biomarkers are
omnipresent in different non-thermophilic soils and
aquatic sediments [especially those where anaerobic
oxidation of methane (AOM) occurs], where they are
supposed to originate from anaerobic bacteria
involved in sulfur and/or methane cycles and in
carbonate precipitation [2]. To date, this biological
origin is not demonstrated and the physiological role
of DGDs remains unknown.
The lipid composition of a newly isolated
hydrocarbon-degrading marine SRB, able to grow
between 20°C and 40°C, is dominated by nonisoprenoid
mono- and di-ethers of glycerol. The
chemical composition of ether lipids appears strongly
dependent on that of the growth substrate. Ethers
formed during growth on mid-chain n-alkenes (C14-
C16) have alkyl chains in the same carbon range,
whereas growth on shorter substrates (pyruvate,
octanoate, etc.) generally yields a more complex
mixture of DGDs. Interestingly, the fatty acid
composition of the strain resembles that of the ether
alkyl chains, suggesting a biosynthetic link between
both classes of compounds. Cultures performed with
synthetic (per)deuterated n-alkenes support these
links by unambiguously demonstrating the direct
incorporation of degradation intermediates [i.e.
corresponding labelled alcohols and (branched-) fatty
acids] into glycerol monoether/monoester and diether
lipids (Fig. 1).
R
R CH2OH
glycerol
diethers
sn-Glycerol-3-P
R COOH
+
ether/
ester
H
HO O
P
10-Me branching
10
�-oxidation
HO
R COOH
R COOH
Fig. 1. Formation of glycerol (di)ethers during the anaerobic
oxidation of n-alkenes by a newly isolated mesophilic SRB.
Besides describing the first production of diether
lipids in a mesophilic and heterotrophic anaerobic
bacterium, our work further extends the metabolic
pathways of unsaturated hydrocarbons in anaerobic
environments. The major geochemical and
biochemical implications of these findings and the
comparison of this strain with SRB involved in AOM
and/or carbonate precipitation will be discussed.
References
[1] Weijers, J.W., Schouten, S., Hopmans, E.C.,
Geenevasen, J.A., David, O.R., Coleman, J.M., et al. (2006)
Environmental Microbiology 8, 648-657.
[2] Bradley, A.S., Fredricks, H., Hinrichs K.-U.,
Summons, R.E. (2009) Organic Geochemistry 40, 1169-
1178.
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