Microbial community in a sediment-hosted CO ₂ lake of the southern Okinawa Trough hydrothermal system

Abstract

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 CO 2 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 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 CO2 lake, decreasing to strikingly low cell numbers (10 7 cm ؊3 ) at the liquid CO2͞CO2-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 CO2 and͞or CH4 dominate the liquid CO2 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 CO2 reservoirs as potential microbial habitats on early Earth and other celestial bodies.anaerobic oxidation of methane ͉ chemolithotroph ͉ CO2 disposal ͉ CO 2 hydrate ͉ liquid CO2

Hydrothermal Activity in the Okinawa Trough Back-Arc Basin: Geological Background and Hydrothermal Mineralization

“…Venting of clear fluid with the highest temperature of 220 C was observed at the foot of the mound, which was accompanied with discharge of significant amount of liquid CO 2 droplets. Liquid CO 2 emanation from altered sediment has been observed in many places around the active hydrothermal mounds (Inagaki et al 2006;Konno et al 2006). In the southern part of the hydrothermal field (the Abyss Vent site), diffusive fluid venting was observed from the seafloor which is covered with sediment associated whitish hydrothermal crusts (Inagaki et al 2006).…”

“…Liquid CO 2 emanation from altered sediment has been observed in many places around the active hydrothermal mounds (Inagaki et al 2006;Konno et al 2006). In the southern part of the hydrothermal field (the Abyss Vent site), diffusive fluid venting was observed from the seafloor which is covered with sediment associated whitish hydrothermal crusts (Inagaki et al 2006). Further south, inactive or diffuse venting from small chimney structures has been recognized, although the area has not been well explored.…”

“…Observations during dive surveys indicate the elongated valley is covered mainly with muddy sediment, except for active hydrothermal sites, and that the northern slope of the valley has volcanic breccia . A diverse style of fluid emanations occurs within the Daiyon-Yonaguni Knoll hydrothermal field (Inagaki et al 2006;Konno et al 2006;Suzuki et al 2008). A large chimney-mound complex called the Tiger site, which is approximately 10-m high, is located near the boundary between the slope of the knoll and sediment seafloor at water depth of~1,370 m. Vigorous venting of blackish-smoky fluids up to 328 C has been recorded from the basal part of the mound complex, which seems to mark the central part of the present hydrothermal activity in the field.…”

Gas geochemical characteristics of hydrothermal plumes at the HAKUREI and JADE vent sites, the Izena Cauldron, Okinawa Trough

“…Another six hydrothermal vent sites in the Okinawa Trough were found subsequently: CLAM (Gamo et al, 1991), MinamiEnsei (Chiba et al, 1993), Iheya North (Chiba et al, 1996;Nakagawa et al, 2005), Hatoma Knoll (Nakano et al, 2001), Yonaguni Knoll IV (Kishida et al, 2004;Konno et al, 2006;Inagaki et al, 2006;Hongo et al, 2007;Suzuki et al, 2008;Nunoura and Takai, 2009), and HAKUREI (Ishibashi et al, 2009). A notable geological Suzuki et al, 2008). origin of the excess methane at sediment-related hydrothermal system was explained by methane production through thermal decomposition of sedimentary organic matter (e.g., Ishibashi et al, 1995).…”

Caldisericum exile gen. nov., sp. nov., an anaerobic, thermophilic, filamentous bacterium of a novel bacterial phylum, Caldiserica phyl. nov., originally called the candidate phylum OP5, and description of Caldisericaceae fam. nov., Caldisericales ord. nov. and Caldisericia classis nov.

“…The candidate phylum OP5 was represented originally by environmental clone sequences retrieved from the Obsidian Pool in Yellowstone National Park (Hugenholtz et al, 1998a) and indicated an independent phylum-level lineage in the domain Bacteria (Hugenholtz et al, 1998a, b;Rappé & Giovannoni, 2003). Since then, environmental clone sequences belonging to this phylum have been detected in various environments (Dojka et al, 1998;Humayoun et al, 2003;Inagaki et al, 2006;Kaksonen et al, 2004;Ley et al, 2006;Skirnisdottir et al, 2000;Teske et al, 2002). Strain AZM16c01 T was the first cultivable isolate accommodated in OP5.…”