Microbial life discovered deep down

At a depth of nearly 2,5 kilometres beneath the seafloor scientists have found proof of active microbial life.

2015.07.29 | Maj Thimm Carlsen

This photo is of scanning electron microscopy and shows microbes collected from deep beneath the seafloor, around 2 kilometres down, enriched using a continuous flow bioreactor producing methane with powdered coals as the energy source. The image is magnified 5000 times. (Photo: Hiroyuki Imachi, JAMSTEC)

80 km off the coast of the Shimokita Peninsula, Japan, scientists have drilled deeper into the seabed than ever before to explore the life at one of the earth’s largest ecosystems: the deep sub-seafloor biosphere. During the Integrated Ocean Drilling Program (IODP) Expedition 337, biogeochemist Dr. Clemens Glombitza and microbiologist Prof. Dr. Mark Lever (now ETH Zürich) from the Center for Geomicrobiology, Aarhus University, were on board the Japanese drilling vessel Chikyu together with an international team of scientists. Co-chief scientists of Expedition 337 were Dr. Fumio Inagaki, Japan Agency for Marine-Earth Science and Technology (JAMSTEC) and Prof. Kai-Uwe Hinrichs, Center for Marine Environmental Science (MARUM) at the University of Bremen, Germany.  The aim of the expedition was to explore the deep biosphere in up to 2.5 km deeply buried sediments harboring imbedded coalbeds which were buried more than 20 million years ago. The results of their study prove the existence of active microbial life in these deeply buried sediments and were published on the 24 of July in the journal Science.

“This is so far the deepest evidence of microbial life, at least for sediments at the bottom of the ocean” says Clemens Glombitza, postdoctoral researcher at Center for Geomicrobiology, Aarhus University and co-author on the study published in Science.

Watch the movie clip about IODP Expedition 337 on YouTube
made by Luc Riolon and Rachel Seddoh

Turning coal into methane

The discovered microbes live in the up to seven meter thick coalbeds at temperatures around 40-60 °C and produce methane by slowly transforming the ancient buried organic matter of the coals. The microbial community that inhabits these coal-bearing sediments differs strongly from those found in shallower sub-seafloor sediments and is genetically closer to communities typically found in forest soils. This suggests that these communities were retained in the sediment tens of millions of years after burial.

At the limit of life

Although the abundance of microbial cells was increased in the deep coal-bearing layers compared to the surrounding sediments, the numbers were lower than expected based on extrapolations of observations from shallower boreholes at ocean margins.  This finding may indicate that microbial communities inhabiting these deep sediments operate at the lower boundary of the deep sedimentary biosphere although not having reached the final limit. In their report in Science, the authors speculate that the dramatic drop in population size in these deep sediments might be a result of the increase of energetic costs to repair temperature induced damage to microbial DNA and biomolecules. Additionally, also other factors like pressure or sediment porosity might limit the microbial life deep down as US scientist Julie Huber writes in a perspective article in Science.

At the edge of drilling technology

The recovery of drill core samples from such great depth and in particular form sediments hosting large quantities of buried organic material as in coal-beds require a special drilling technique, the so-called “riser drilling”. This technique was initially developed by oil industry to avoid dangerous “blow-outs” where massive amounts of gas are released to the surface. Only recently, this drilling technique became available for scientific drilling operations. The Japanese drilling vessel Chikyu is not only the largest and most modern drilling vessel operating under the IODP; it is also the only research drilling vessel providing a riser drilling system. IODP Expedition 337 not only recovered the deepest drill core samples from below the ocean floor so far, but also pioneered the riser drilling technique in scientific ocean drilling. Only by the use of this advanced technique it was possible to recover scientific samples from deeply buried coal-bearing sediments to study this unique environment.


Exploring deep microbial life in coal-bearing sediment down to ~2.5 km below the ocean floor
Fumio Inagaki, Kai-Uwe Hinrichs, Yusuke Kubo, Marshall W. Bowles, Verena B. Heuer, Wei-Li Hong, Tatsuhiko Hoshino, Akira Ijiri, Hiroyuki Imachi, Motoo Ito, Masanori Kaneko, Mark Alexander Lever, Yu-Shih Lin, Barbara A. Methé, Sumito Morita, Yuki Morono, Wataru Tanikawa, Monika Bihan, Stephen A. Bowden, Marcus Elvert, Clemens Glombitza, Doris Gross, Guy J. Harrington, Tomoyuki Hori, Kelvin Li, David Limmer, Chang-Hong Liu, Masafumi Murayama, Naohiko Ohkouchi, Shuhei Ono, Young-Soo Park, Stephen C. Phillips, Xavier Prieto-Mollar, Marcella Purkey, Natascha Riedinger, Yoshinori Sanada, Justine Sauvage, Glen Snyder, Rita Susilawati, Yoshinori Takano, Eiji Tasumi, Takeshi Terada, Hitoshi Tomaru, Elizabeth Trembath-Reichert, David T. Wang, and Yasuhiro Yamada.
Science magazine, July 24th 2015, doi:10.1126/science.aaa6882 (only for subscribers)

Read more

Go to press release by JAMSTEC

Expedition 337's homepage

Julie Hubert’s perspective piece for Science

Science News

Science Nordic

Videnskab dk (in Danish)

For more information, please contact

Postdoctoral Scientist Clemens Glombitza, Center for Geomicrobiology, Department of Bioscience, Aarhus University, +45 8715 4341/23924367, clemens.glombitza@bios.au.dk


Center for Geomicrobiology, Research news