25th International Meeting on Organic Geochemistry IMOG 2011

P-158
Unusual distribution of long-chain heterocyst glycolipids in an
Icelandic hot spring
Thorsten Bauersachs, Marcel Van der Meer, Stefan Schouten, Jaap Sinninghe Damsté
Royal Netherlands Institute for Sea Research, Texel, Netherlands (corresponding author:thb@gpi.unikiel.de)
Heterocyst glycolipids (HGs) represent novel
biological markers for diazotrophic (N2-fixing)
heterocystous cyanobacteria. These components
surround the heterocysts - specialized cells dedicated
to the fixation of N2 - and act as an effective gas
diffusion barrier that prevents O2 diffusion into the cell
[1]. HGs have recently been used to trace for
diazotrophic heterocystous cyanobacteria in modern
and ancient environments, including coastal microbial
mats as well as lacustrine and marine sediments [2].
The HGs detected in this environments solely
consisted of C26 and C28 diols, triols as well as their
corresponding ketone varieties.
Here, we report on the intact polar lipid (IPL)
composition of a microbial mat growing in a sulfidic
Icelandic hot spring, which was dominated by green
non-sulfur bacteria closely related to Chloroflexus
aurantiacus and the heterocystous filamentous
cyanobacterium Mastigocladus sp. The IPL
composition of the microbial mat was characterized
by the dominance of the glycolipids MGDG, SQDG,
DGDG and the phospholipid PG, which are common
in photosynthetic organisms. In addition, a suite of
components with retention times similar to those
previously reported for heterocyst glycolipids was
present. Based on the mass spectral characteristics,
we identified these components as C30 and C32 HG
triols.
In order to identify the source of these unusual longchain
HGs, we grew a physiologically related strain of
Mastigocladus sp. under nitrogen-depleted conditions
and environmental parameters similar to those
encountered in the Icelandic hot spring. The analysis
of its intact polar lipid content indeed revealed the
presence of the C32 HG triol and thus established
Mastigocladus sp. as the probable source of this longchain
HG (Fig. 1). Surprisingly, no C30 HG triol was
detected in our isolate. The HG composition between
different species and strains of the same genus,
however, might vary and Mastigocladus sp. is thus
the most likely source of both long-chain HG triols in
the hot spring microbial mat.
Heterocystous cyanobacteria have previously been
suggested to vary their HG composition with
temperature in order to compensate for increased O2
fluxes into the heterocyst under elevated ambient
temperatures [3]. Our results suggest that
thermophilic heterocystous cyanobacteria are indeed
characterized by a HG composition that is distinctly
different from what is observed in other moderate and
tropical environments and that the increased chainlength
might be an adaptation to the increased
temperatures in hot springs. In addition, C30 and C32
HG triols have not yet been reported from
cyanobacteria other than Stigonematales suggesting
a possible chemotaxonomic value for the long-chain
heterocyst glycolipids.
Fig. 1. Base peak chromatogram of the total lipid extract of
the heterocystous cyanobacterium Mastigocladus sp.
References
[1] Nichols and Wood (1968) Nature, 217, 767-769
[2] Bauersachs et al. (2010) PNAS, 107, 19190-19194
[3] Staal et al. (2007) Nature, 425, 504-507
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