How Subseafloor Bacteria Survive in Harsh Conditions: Over-Activating DNA Repair

You wouldn't think that much could survive in the deepest parts of the world's oceans. Yet subseafloor bacteria thrive under these harsh conditions. Now, scientists have found that this huge microbial biosphere is alive, dividing, and has adapted by over-activating stress response and DNA-repair mechanisms in order to cope with the hard environment.

Subseafloor sediment contains the Earth's largest habitat for microbial life. In fact, over a third of all of the planet's microbial biomass can be found here. Yet scientists have long wondered whether this huge microbial biosphere was alive and dividing. That's why the scientists wanted to see if they were active in their natural sea-bed situation.

The researchers drilled cores from the continental shelf off of the coast of Peru. Then, they compared gene expression at several depths spanning five to 159 meters below the seafloor. In the end, they found that the expression of DNA repair genes, such as recA, increases with the amount of time the microbes have been buried in the seafloor.

"This is the largest microbial biosphere on Earth, composed of cells living deep beneath the surface," said William Orsi, one of the researchers, in a news release. "We have recently shown for the first time that these cells, the 'deep biosphere,' are actually dividing and not in a dormant state. This means that the deep biosphere is active and due to its sheer size likely plays an important role in global elemental cycles over geological timescales."

So how do the bacteria survive in this environment? They ramp-up coping mechanisms that allow them to survive under high pressures when they're starved of nutrients.

"Subseafloor microbes have adapted to live in especially harsh conditions," said Orsi in a news release. "We found that they significantly overexpress genes involved in cellular stress responses like recA. This gene is central to the bacterial 'SOS response,' which is a way bacteria cope with many different environmental stressors including antibiotics. We have found that subseafloor microbes increasingly express this gene with time after they become 'buried alive' in the subseafloor."

The findings reveal a bit more about this community of bacteria. This could show researchers a bit more about the life in oceans thousands of years ago.

The findings were presented at the Goldschmidt conference in Sacramento California.