Extreme seabed-survival boosts hope of aliens
by Rob Edwards / 28 August 2006

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.

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

Fumio Inagaki*, Marcel M. M. Kuypers, Urumu Tsunogai, Junichiro 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 Boetius

*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 Japan; Department of Earth and Planetary Sciences, Faculty of Sciences, Kyushu University, Fukuoka Japan; ||Institute of Geology and Geoinformation, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan; and **Department of Earth Science, Okayama University, Okayama Japan

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.

correspondence should be addressed to: inagaki [at] jamstec [dot] go [dot] jp

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