25th International Meeting on Organic Geochemistry IMOG 2011

P-175
Molecular and isotopic biosignatures in altered and unaltered
hydrothermal precipitates of the southern Mid-Atlantic Ridge
Sascha Herrlich 1 , Martin Blumenberg 2 , Walter Michaelis 1 , Anne Dreier 3 , Richard Seifert 1
1 Institute of Biogeochemistry and Marine Chemistry, University of Hamburg, Hamburg, Germany,
2 Department of Geobiology, Geoscience Centre (GZG), Georg-August-University of Göttingen, Göttingen,
Germany, 3 Department General Microbiology, Institute of Microbiology and Genetics, Georg-August-
University of Göttingen, Göttingen, Germany (corresponding author:richard.seifert@zmaw.de)
Deep sea hydrothermal systems are outstanding
geobiological habitats. Steep redox gradients
between hydrothermal fluids and sea water offer an
excellent basis for chemoautotrophic microorganisms
and massive metal sulphide precipitates provide a
long-lasting energy source for Fe/S-oxidizers.
Recent studies on autochthonous microbial
communities of unaltered hydrothermal precipitates
using chemical structures and stable isotope ratios of
organic compounds revealed specific biomarkers and
indicated an extraordinary phylogenetic and metabolic
diversity. [1,2]. However, similar studies on microbial
communities invading hydrothermal deposits after the
active state are almost missing.
In this study we compare molecular biosignatures
enclosed in an almost unaltered fresh metal sulphide
precipitated by an active black smoker emitting
extraordinarily hot fluids with those of a subrecent
altered chimney having been exposed to seawater for
an extended time period.
Samples were obtained in 2009 by a remotely
operated vehicle (ROV Kiel 6000) from 3000m water
depth during R/V Meteor cruise M78/2 between 5°
und 9°S at the Mid-Atlantic Ridge.
The observed differences in distribution and isotopic
composition of biomarkers between the active and the
altered black smoker mirrors the change from the
microbial community inhabiting the active
hydrothermal system to a secondary community
dominant during early diagenetic alteration of the
precipitates.
For the active smoker sample, high concentrations of
fatty acids strongly enriched in 13 C (� 13 C-values of
about -10 ‰) point to chemolithoautotrophic,
hydrogen-oxidizing bacteria using the rTCA-cycle for
carbon fixation (e.g., Hydrogenobacter, Aquifex [3].
By contrast, the altered black smoker contains high
concentrations of 13 C-depleted iso-, anteiso-, and mid
chain-branched penta- and heptadecanoic fatty acids.
Some of these compounds might originate from
sulphur-oxidizing bacteria fixing carbon via the Calvin
cycle as reported for relatives of Thiobacillus,
Acidithiobacillus [3].
Both samples contain a huge variety of bacterial and
archaeal Dialkyl Glycerol Diethers (DAGE). The wide
range of � 13 C-values of the DAGE in both samples
points to consortia of bacteria and archaea using
different carbon fixation pathways.
13 C-depleted
hydroxyarchaeol (� 13 C of -70‰) indicates
methanotrophic archaea (ANME-2) in the altered
sample.
Interestingly there was a regular C25 isoprenoid
analyzed after ether cleavage suggested to originate
from C25,25 or C20,25 archaeol. The latter is described
from halophilic archaea, while the former was
reported from the aerobic, hyperthermophilic
crenarchaeon Aeropyrum pernix, isolated from a
solfataric vent [4].
For the altered black smoker sample, high amounts of
acyclic, monocyclic and bicyclic biphytanes were
released by cleavage of ether bonds from archaeal
Glycerol Dialkyl Glycerol Tetraethers (GDGT). Among
clear signals from methanogens, the prevalence of
monocyclic and bicyclic biphytanes indicated
contributions from mesophilic to moderately
thermophilic, Fe-oxidizing archaeon Ferroplasma
acidophilum [5] and/or from the thermoacidophilic
sulphur oxidizing archaeon.
Preliminary lipid data of selected, yet unstudied
extremophilic isolates, accompanying our work on
hydrothermal sulfides, indicate that e.g. the nitratereducing
thermophilic Caldithrix abyssi is an important
member of the microbial community in the altered
sulfide.
References
[1] Blumenberg M, Seifert R, Petersen S, Michaelis
W. 2007. Geobiology 5:435-450.
[2] Bradley AS, Hayes JM, Summons RE. 2009.
Geochim Cosmochim Acta 73:102-118.
[3] Naraoka H., Uehara T., Hanada S., Kakegawa T.
2009. Org. Geochem., 41, 398-403.
[4] Sako Y., et al. 1996. J. System. Bacteriol., 46,
1070–1077
[5] Golyshina O. V., Timmis K. N. 2005. Environ
Microbiol., 7, 1277–1288.
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