Increasing levels Of CO(2) in the atmosphere are expected to cause climatic change with negative effects on the earth's ecosystems and human society. Consequently, a variety of CO(2) disposal options are discussed, including injection into the deep ocean. Because the dissolution Of CO(2) in seawater will decrease ambient pH considerably, negative consequences for deep-water ecosystems have been predicted. Hence, ecosystems associated with natural Co(2) reservoirs in the deep sea, and the dynamics of gaseous, liquid, and solid CO(2) 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 CO(2) lake at the Yonaguni Knoll IV hydrothermal field, southern Okinawa Trough. We found high abundances (> 10(9) CM(-3)) of microbial cells in sediment pavements above the CO(2) lake, decreasing to strikingly low cell numbers (107 CM-3) at the liquid CO(2)/CO(2)-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 (13)C-depleted archaeal and bacterial lipid biomarkers suggest that microorganisms assimilating CO(2) and/or CH(4) dominate the liquid CO(2) and CO(2)-hydrate-bearing sediments. Clearly, the Yonaguni Knoll is an exceptional natural laboratory for the study of consequences of CO(2) disposal as well as of natural CO(2) reservoirs as potential microbial habitats on early Earth and other celestial bodies.
National Academy of Sciences. Proceedings, 2006, Vol 103, Issue 38, p. 14164-14169