Extreme seabed-survival boosts hope of aliens

22:00 28 August 2006 news service
Rob Edwards

Microbes discovered by a lake of liquid carbon dioxide under the sea
off Taiwan could help us locate life on Mars, researchers say.

Japanese and German researchers have found billions of bacteria and
other tiny organisms living in a layer of sediment which traps the CO2
under the seabed. Their survival in such a hostile natural environment
suggests that something similar could be happening on other planets.

If water and CO2 are present below the surface in polar environments,
says Fumio Inagaki at the Japan Agency for Marine-Earth Science and
Technology in Yokosuka, “I expect that life signatures utilising
chemical materials and CO2 for growth might be found.”

Inagaki’s team and researchers at the Max Planck Institute for Marine
Microbiology in Bremen, Germany, investigated an area at the southern
end of the Okinawa Trough, about 1400 metres under the East China Sea.
There, hot black sulphurous fluids are vented into the water from two
seabed “chimneys” known as Tiger and Lion, a stunning phenomenon
captured on video by the research team.

Surreal sight

The microbes were discovered 50 m south of the chimneys in samples
taken from the crust of sediment covering a lake of liquid CO2. The
video also shows a clear stream of CO2 bubbles escaping from the hole
made by the researchers’ sample corer.

This is a sight that few people have ever seen, says Kenneth Nealson at
the University of Southern California in Los Angeles, US. It looks
“almost surreal”, he says in a commentary accompanying the research in
the journal Proceedings of the National Academy of Sciences.

Inagaki hopes that his research will also help plans to dispose of
climate-wrecking CO2 by injecting it into the seabed. Care needs to be
taken to make sure that acidification does not damage ecosystems, he
told New Scientist.

Journal reference: Proceedings of the National Academy of Sciences
(DOI: 10.1073/pnas.0606083103)

From the Cover
Microbial community in a sediment-hosted CO2 lake of the southern
Okinawa Trough hydrothermal system

Fumio Inagaki*,,, Marcel M. M. Kuypers, Urumu Tsunogai, Jun-ichiro
Ishibashi¶, Ko-ichi Nakamura||, Tina Treude, Satoru Ohkubo, Miwako
Nakaseama¶, Kaul Gena**, Hitoshi Chiba**, Hisako Hirayama*, Takuro
Nunoura*, Ken Takai*, Bo B. Jørgensen, Koki Horikoshi*, and Antje

*Subground Animalcule Retrieval (SUGAR) Program, Extremobiosphere
Research Center, Japan Agency for Marine-Earth Science and Technology
(JAMSTEC), Yokosuka 237-0061, Japan;  Max Planck Institute for Marine
Microbiology, 28359 Bremen, Germany;  Department of Earth and Planetary
Sciences, Graduate School of Science, Hokkaido University, Sapporo
060-0810, Japan; ¶Department of Earth and Planetary Sciences, Faculty
of Sciences, Kyushu University, Fukuoka 812-8581, Japan; ||Institute of
Geology and Geoinformation, National Institute of Advanced Industrial
Science and Technology (AIST), Tsukuba 305-8567, Japan; and
**Department of Earth Science, Okayama University, Okayama 700-8530,

Communicated by Norman H. Sleep, Stanford University, Stanford, CA,
July 21, 2006 (received for review March 10, 2006)

Increasing levels of CO2 in the atmosphere are expected to cause
climatic change with negative effects on the earth’s ecosystems and
human society. Consequently, a variety of CO2 disposal options are
discussed, including injection into the deep ocean. Because the
dissolution of CO2 in seawater will decrease ambient pH considerably,
negative consequences for deep-water ecosystems have been predicted.
Hence, ecosystems associated with natural CO2 reservoirs in the deep
sea, and the dynamics of gaseous, liquid, and solid CO2 in such
environments, are of great interest to science and society. We report
here a biogeochemical and microbiological characterization of a
microbial community inhabiting deep-sea sediments overlying a natural
CO2 lake at the Yonaguni Knoll IV hydrothermal field, southern Okinawa
Trough. We found high abundances (>109 cm-3) of microbial cells in
sediment pavements above the CO2 lake, decreasing to strikingly low
cell numbers (107 cm-3) at the liquid CO2/CO2-hydrate interface. The
key groups in these sediments were as follows: (i) the anaerobic
methanotrophic archaea ANME-2c and the Eel-2 group of
Deltaproteobacteria and (ii) sulfur-metabolizing chemolithotrophs
within the Gamma- and Epsilonproteobacteria. The detection of
functional genes related to one-carbon assimilation and the presence of
highly 13C-depleted archaeal and bacterial lipid biomarkers suggest
that microorganisms assimilating CO2 and/or CH4 dominate the liquid CO2
and CO2-hydrate-bearing sediments. Clearly, the Yonaguni Knoll is an
exceptional natural laboratory for the study of consequences of CO2
disposal as well as of natural CO2 reservoirs as potential microbial
habitats on early Earth and other celestial bodies.

anaerobic oxidation of methane | chemolithotroph | CO2 disposal | CO2
hydrate | liquid CO2

Author contributions: F.I., B.B.J., K.H., and A.B. designed research;
F.I., M.M.M.K., U.T., J.-i.I., K.-i.N., T.T., S.O., M.N., K.G., H.C.,
H.H., T.N., K.T., and A.B. performed research; F.I., M.M.M.K., U.T.,
J.-i.I., K.-i.N., T.T., S.O., M.N., K.G., H.C., and A.B. analyzed data;
and F.I., M.M.M.K., and A.B. wrote the paper.
Conflict of interest statement: No conflicts declared.

Data deposition: The 16S rRNA, mcrA, and cbbL gene sequences reported
in this paper have been deposited in the DNA Data Bank of
Japan/European Molecular Biology Laboratory/GenBank databases
(accession nos. AB252422-AB252455).

See Commentary on page 13903.

To whom correspondence should be addressed. E-mail:
inagaki [at] jamstec [dot] go [dot] jp

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