Ancient Bacteria Still Busy In The Deep

Twenty million years ago, forested land rich in coal was gradually subsumed by ocean off the coast of what is now Japan. This layer of coal, buried more than a mile below the Pacific seafloor, still hosts an active microbial population from that ancient terrestrial environment, reports a team of researchers led by Fumio Inagaki of the Japan Agency for Marine-Earth Science & Technology, in Kochi, and Kai-Uwe Hinrichs of the University of Bremen, in Germany (Science 2015, DOI: 10.1126/science.aaa6882). The team took core samples 1.5 miles into the seafloor and found that the microbial population in the deepest portion was producing methane using coal as a carbon and energy source. On the basis of isotope analysis, DNA sequencing, and other analyses, the team argues that the microbes are not endemic to marine environments but hark back to the coal layer’s terrestrial origins, in the late Paleogene era, 20 million years ago. This report “marks the deepest detection of active life to date,” and there’s likely even more life lying in deeper layers to be discovered, comments Julie A. Huber of the Marine Biological Laboratory in Woods Hole, Mass., in an associated commentary in Science.