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Published July 24, 2015 | Supplemental Material
Journal Article Open

Exploring deep microbial life in coal-bearing sediment down to ~2.5 km below the ocean floor

Abstract

Microbial life inhabits deeply buried marine sediments, but the extent of this vast ecosystem remains poorly constrained. Here we provide evidence for the existence of microbial communities in ~40° to 60°C sediment associated with lignite coal beds at ~1.5 to 2.5 km below the seafloor in the Pacific Ocean off Japan. Microbial methanogenesis was indicated by the isotopic compositions of methane and carbon dioxide, biomarkers, cultivation data, and gas compositions. Concentrations of indigenous microbial cells below 1.5 km ranged from <10 to ~10^4 cells cm^(−3). Peak concentrations occurred in lignite layers, where communities differed markedly from shallower subseafloor communities and instead resembled organotrophic communities in forest soils. This suggests that terrigenous sediments retain indigenous community members tens of millions of years after burial in the seabed.

Additional Information

© 2015 American Association for the Advancement of Science. Received for publication 23 January 2015. Accepted for publication 10 June 2015. The authors are grateful to IODP and the Ministry of Education, Culture, Sports, Science and Technology of Japan for providing an opportunity to explore the deep coal-bed biosphere off Shimokita during Expedition 337. We thank all crews, drilling team members, lab technicians, and scientists on the drilling vessel Chikyu for supporting core sampling and onboard measurements during Chikyu shakedown cruise CK06-06 and IODP Expedition 337. The authors thank J. A. McKenzie and K. H. Nealson for useful discussions during project design; S. Fukunaga, S. Hashimoto, A. Imajo, Y. Saito, S. Tanaka, K. Uematsu, and N. Xiao for assistance in microbiological analyses; and D. Gruen for technical assistance during clumped isotope analysis. This work was supported in part by the Japan Society for the Promotion of Science (JSPS) Strategic Fund for Strengthening Leading-Edge Research and Development (to F.I. and JAMSTEC), the JSPS Funding Program for Next Generation World-Leading Researchers (grant no. GR102 to F.I.), the JSPS Grants-in-Aid for Science Research (no. 26251041 to F.I., no. 24770033 to T.H., no. 24687011 to H.I., no. 26287142 to M.I., no. 25610166 to M.K., and nos. 24651018 and 24687004 to Y.M.), the European Research Council (Advanced Grant no. 247153 to K.-U.H.), the Deutsche Forschungsgemeinschaft trough project HI 616/16 (to K.-U.H.) through MARUM–Cluster of Excellence 309, and NSF (no. EAR-1250394 to S.O). All shipboard and shore-based data presented in this manuscript are archived and publicly available online in the IODP Expedition 337 Proceedings (6) through the J-CORES database (http://sio7.jamstec.go.jp/j-cores.data/337/C0020A/) and the PANGAEA database (http://doi.pangaea.de/10.1594/PANGAEA.845984). This is a contribution to the Deep Carbon Observatory.

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August 20, 2023
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