Deep in the ocean’s sediments dwell half of the microorganisms on Earth. Little has been known, however, about what these bacteria and fungi are up to. It is a question that matters in understanding global climate change because there are lots of nutrients deep in the open floor — including carbon. If those microbial deep-sea inhabitants are dormant, carbon and other nutrients are likely to stay put. If they are alive and active, the microbes may be cycling that stuff back into the ocean.
Now, researchers have a clue. Scientists from the Woods Hole Oceanographic Institution and the University of Delaware used genomic tools to analyze material from samples collected from sediment off the coast of Peru. Instead of sequencing the genomes of the microscopic organisms, which would have told them only what bacteria were down there, the researchers analyzed which genes were switched on. They found about 300,000 active genes, many involved in the process by which cells multiply, suggesting they are, indeed, active.
“These sediments of the ocean actually contain the world’s largest reservoir of organic carbon, from marine ‘snow’ particles, organic stuff that’s sinking down through the water and gradually builds up over geological time,” said William Orsi, a guest investigator at Woods Hole who led the work published Wednesday in the journal Nature. “How are these microbes in the deep biosphere’s activities relevant to global warming or the amount of carbon dissolved in the ocean? That is really unknown at this point and that deserves further study.”