부산대학교 도서관

Increasing levels of C[O.sub.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 C[O.sub.2] disposal options are discussed, including injection into the deep ocean. Because the dissolution of C[O.sub.2] in seawater will decrease ambient pH considerably, negative consequences for deep-water ecosystems have been predicted. Hence, ecosystems associated with natural C[O.sub.2] reservoirs in the deep sea, and the dynamics of gaseous, liquid, and solid C[O.sub.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 C[O.sub.2] lake at the Yonaguni Knoll IV hydrothermal field, southern Okinawa Trough. We found high abundances (>[10.sup.9] [cm.sup.-3]) of microbial cells in sediment pavements above the C[O.sub.2] lake, decreasing to strikingly low cell numbers ([10.sup.7] [cm.sup.-3]) at the liquid C[O.sub.2]/C[O.sub.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 [sup.13]C-depleted archaeal and bacterial lipid biomarkers suggest that microorganisms assimilating C[O.sub.2] and/or C[H.sub.4] dominate the liquid C[O.sub.2] and C[O.sub.2]-hydrate-bearing sediments. Clearly, the Yonaguni Knoll is an exceptional natural laboratory for the study of consequences of C[O.sub.2] disposal as well as of natural C[O.sub.2] reservoirs as potential microbial habitats on early Earth and other celestial bodies. anaerobic oxidation of methane | chemolithotroph | C[O.sub.2] disposal | C[O.sub.2] hydrate | liquid C[O.sub.2]