25th International Meeting on Organic Geochemistry IMOG 2011

O-24
A biological source for the orphan branched tetraethers
ubiquitously occurring in soil and coastal marine and lake
sediments
Jaap Sinninghe Damste 1,2 , Irene Rijpstra 1 , Johan Weijers 2 , Ellen Hopmans 1 , Baerbel
Foesel 3 , Joerg Overmann 3 , Svetlana Dedysh 4
1 NIOZ Netherlands Institute for Sea Research, Department of Marine Organic Biogeochemistry, Den Burg,
Netherlands, 2 Utrecht University, Department of Earth Sciences, Geochemistry,, Utrecht, Netherlands,
3 Leibniz-Institut DSMZ - Deutsche Sammlung von Mikroorganismen und Zellkulturen, Braunschweig,
Germany, 4 S.N. Winogradsky Institute of Microbiology, Russian Academy of Sciences, Moscow, Russian
Federation (corresponding author:jaap.damste@nioz.nl)
Global climate change is a topic of major interest as it
has a large impact on human societies. Detailed
reconstruction of past climates, especially temperature,
is, therefore, of considerable importance.
Several organic proxies are available to reconstruct
absolute sea surface temperatures. Continental
temperature reconstructions, however, are hampered
by a lack of quantitative temperature proxies and,
consequently, are often qualitative rather than
quantitative. Recently, we discovered a new
quantitative continental temperature proxy, the
MBT/CBT index, which is based on the distribution of
branched glycerol dialkyl glycerol tetraethers (GDGT;
e.g. 1) membrane lipids of bacteria residing in soil and
peat [1]. Their composition is a function of annual
mean air temperature and pH. These lipids are
transported by rivers to the ocean and deposited in
marine sediments. Determination of the MBT/CBT
index in sediment cores from river fans can, thus,
potentially be used to reconstruct continental, river
basin-integrated, temperatures from a marine record
in front of large river outflows. For a full understanding
and validation of this proxy, the microbial origin of
branched GDGTs needs to be elucidated. In a study
of a Swedish peat, molecular ecological data pointed
to the potential of Acidobacteria, a highly diverse
phylum of the Bacteria, to biosynthesize branched
GDGTs but examined cultures did not reveal the
presence of branched GDGTs. In this study, we
systematically investigated 17 different, available and
newly isolated, cultured strains representing 13
different species of subdivisions 1 and 3 of the
Acidobacteria.
The distribution of membrane lipids were examined by
hydrolysis and GC/MS and by HPLC/MS of intact
polar lipids (IPLs). Upon both acid and base
hydrolysis of total cell material the uncommon
membrane-spanning lipid, 13,16-dimethyl octacosanedioic
acid (iso diabolic acid, 2), was released
from all studied acidobacteria in substantial amounts
(22-43% of all fatty acids). This lipid has previously
only been encountered in thermophilic Thermoanaerobacter
species but bears a structural
resemblance to the alkyl chains of bacterial glycerol
dialkyl glycerol tetraethers (GDGT) that occur
ubiquitously in peat and soil. As reported previously,
most species also contained iso C15 and C16:1ω7C as
major fatty acids but the presence of iso diabolic acid
was unnoticed in previous studies, most probably
because the complex lipid that contained this moiety
was not extractable from the cells and iso diabolic
acid only be released by hydrolysis. Direct analysis of
intact polar lipids in the Bligh Dyer extract of three
Acidobacterial strains did indeed not reveal the
presence of membrane spanning lipids. In two of the
17 strains ether-bound iso diabolic acid was detected
after a hydrolysis of the cells, including one branched
GDGT (1), containing iso diabolic acid-derived alkyl
chains. Although this represents an important step in
the identification of the biological source of the orphan
branched GDGTs, their distribution in soils is more
complex and the presence of additional (Acido)bacteria
have to explain the presence of the full
complement of branched GDGTs in soil and coastal
marine and lake sediments.
References
[1] Weijers, J.W.H., Schouten S., van den Donker
J.C., Hopmans E.C., Sinninghe Damsté J.S., 2007.
Geochim. Cosmochim. Acta 71, 703-713.
[2] Weijers J.W.H., Panoto E., van Bleijswijk J.,
Schouten S., Rijpstra W.I.C., Balk M., Stams A.J.M.,
Sinninghe Damsté J.S. 2009. Geomicrobiol. J. 26,
402-414.
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