The Ocean Drilling Program (ODP) was funded by the U.S. National Science Foundation and 22 international partners (JOIDES) to conduct basic research into the history of the ocean basins and the overall nature of the crust beneath the ocean floor using the scientific drill ship JOIDES Resolution. Joint Oceanographic Institutions, Inc. (JOI), a group of 18 U.S. institutions, was the Program Manager. Texas A& M University, College of Geosciences was the Science Operator. Columbia University, Lamont-Doherty Earth Observatory provided Logging Services and administered the Site Survey Data Bank. Any opinions, findings, and conclusions or recommendations expressed in these documents are those of the author(s) and do not necessarily reflect the views of the National Science Foundation, the participating agencies, Joint Oceanographic Institutions, Inc., Texas A& M University, or Texas A& M Research Foundation.Studies of deeply buried, sedimentary microbial communities and associated biogeochemical processes during Ocean Drilling Program Leg 201 showed elevated prokaryotic cell numbers in sediment layers where methane is consumed anaerobically at the expense of sulfate. Here, we show that extractable archaeal rRNA, selecting only for active community members in these ecosystems, is dominated by sequences of uncultivated Archaea affiliated with the Marine Benthic Group B and the Miscellaneous Crenarchaeotal Group, whereas known methanotrophic Archaea are not detectable. Carbon flow reconstructions based on stable isotopic compositions of whole archaeal cells, intact archaeal membrane lipids, and other sedimentary carbon pools indicate that these Archaea assimilate sedimentary organic compounds other than methane even though methanotrophy accounts for a major fraction of carbon cycled in these ecosystems. Oxidation of methane by members of Marine Benthic Group B and the Miscellaneous Crenarchaeotal Group without assimilation of methane carbon provides a plausible explanation. Maintenance energies of these subsurface communities appear to be orders of magnitude lower than minimum values known from laboratory observations, and ecosystem-level carbon budgets suggest that community turnover times are on the order of 100 to 2,000 years. Our study provides clues about the metabolic functionality of two cosmopolitan groups of uncultured Archaea.
