One of the largely unexplored habitats on Earth lies under the ocean: the sediments, rocks, and fluids layered under the pressure of a gigantic basin of water. What lives down there, and how deep does life go? What strategies do microbes have for surviving in this environment? MBL Associate Scientist Julie Huber is among the people asking these questions, and this week she contributes a commentary in the journal Science on a team’s discovery of the deepest subseafloor life yet.
Julie Huber. Credit: Diana Kenney
Using a drilling system aboard a research vessel off the Shimokita Peninsula of Japan, the international team “drilled the deepest scientific borehole to date to examine the abundance, taxonomic composition, and biosignatures of subseafloor microbial communities in sediments from 400 to almost 2,500 meters (about 1.5 miles) beneath the seafloor,” Huber writes. They detected microbial life at all depths, including methane-producing archaea in deeply buried coal-bed deposits.
As expected from prior studies, the concentration of microbes decreased steadily with depth in the shallow subseafloor layers. However, microbes were scarce–barely detectable—below about 1,500 meters. This was surprising, given that temperatures in the deep samples didn’t exceed ~60 degrees C, “well within the growth range of most microbes,” and “both carbon and hydrogen are plentiful energy sources, particularly in the coal bed layers,” Huber writes.
“Why so little life, then?” Huber writes. “It is difficulties with biomolecule repair, as the authors suggest, or something else like porosity or pressure? Uncovering what limits the biomass in this unusual environment will certainly be a focus of future studies.”
Huber is associate director of the MBL’s Josephine Bay Paul Center, as well as associate director of the NSF Science and Technology Center for Dark Energy Biosphere Investigations (C-DEBI).
Huber JA (2015) Making methane down deep. Science 349: 376-377.
Inagaki F et al (2015) Exploring deep microbial life in coal-bearing sediment down to ~2.5 km below the ocean floor. Science 349: 420-424.
Article in The Washington Post quoting Huber on Inagaki et al.