The Joides Resolution  heads to sea from Ponta Delgada, Azores to drill sediments on Expedition 339. The sediments were used in the study of microbial gene activity.
The Joides Resolution heads to sea from Ponta Delgada, Azores to drill sediments on Expedition 339. The sediments were used in the study of microbial gene activity.
courtesy of Joseph Russell, University of Delaware

Deep within the ocean’s sediments dwell half the microorganisms on Earth. Little has been known, however, about what these bacteria and fungi are up to. It’s 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 six coffee-cup-sized cores collected from sediments 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 300,000 active genes, many involved in the process by which cells multiply, suggesting that 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.”

Advertisement - Continue Reading Below

Orsi said that he hopes to grow the bacteria and other microorganisms found in the sediment in the laboratory. He will subject them to similar conditions as the ones found in the deep ocean and try to gain insight into how they may be cycling nutrients back into the ocean.

The snapshot of gene activity in remote environments can provide a picture of what life is doing down there—a question that has thus far only been answered by theory and models.