25th International Meeting on Organic Geochemistry IMOG 2011

P-174
Distinct microbial inventories in terrestrial mud volcanoes of
Northern Italy controlled by the source and composition of
emitted fluids
Christina Heller 1 , Martin Blumenberg 1 , Christoph Wrede 2 , Michael Hoppert 2 , Marco
Taviani 3 , Joachim Reitner 1
1 Geoscience Centre, University of Goettingen, Goettingen, Germany, 2 Institute of Microbiology and Genetics,
University of Goettingen, Goettingen, Germany, 3 ISMAR-CNR, Bologna, Italy (corresponding
author:cheller1@gwdg.de)
Mud volcanoes are geological structures that occur in
terrestrial and marine environments worldwide and
are caused by various geological processes e.g.
tectonic accretion and faulting. In Italy such fluid
venting structures occur along the external
compressional margin of the Apennine chain, where
the mud volcanoes are distributed along two belts [1].
The natural Salse di Nirano (near Modena) is one of
the largest mud volcano areas in Italy, emitting gas
with approximately 99 % methane and only minor
amounts of higher hydrocarbons. The fluids seeping
out in Nirano pass through geological formations from
the Jurassic to the lower Pleistocene [2]. In doing so,
the mud is getting enriched in various electron
acceptors (e.g. SO4 2- , NO2 - /NO3 - , O2), potentially
fueling microbial aerobic and anaerobic oxidation of
hydrocarbons, in particular methane [3,4,5]. A
second, smaller and geologically distinct mud volcano
area is situated in Puianello (near Modena). In
Puianello methane concentrations in the gases are
lower ~48 % and, in contrast to Nirano, the fluids do
not cross Messinian formations, thus, ions like sulfate
are relatively lower in concentration.
Our biomarker and molecular microbiological (16S
rDNA) data show that microbial communities in the
different mud volcanoes are distinct. We found signals
of various eukaryotes, bacteria and archaea at both
sites. In Nirano, however, specific bacterial dialkyl
glycerol diethers (DAGE; in particular ai15/ai15- and
16/16-DAGE) were found which are putatively
sourced by sulfate-reducing bacteria (SRB) [6,7,8].
The presence of archaea is evidenced by archaeol
and hydroxyarchaeol and isotopic analyses of SRBderived
bacterial DAGE as well as hydroxyarchaeol
demonstrated 13 C-depletions with δ 13 C values low as -
54‰, suggesting an involvement of the source
organisms in the sulfate-dependent anaerobic
turnover of methane. By contrast, typical SRBbiomarkers
were absent in sulfate-poor mud
volcanoes in Puianello. But, various 13 C-depleted
hopanoids e.g. 17β(H)21β(H)-bishomohopanol
17β(H)21β(H)-bishomohopanoic acid and 3Me-
17β(H)21β(H)-bishomohopanol were highly abundant.
Since the latter are typical biomarkers for aerobic
methanotrophs, those bacteria appear to be keyplayers
in this environment.
Our data demonstrate a high microbial and metabolic
diversity in terrestrial mud volcanoes in Italy, which is
most likely controlled by different geological settings
and thus mud compositions.
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