Researchers found oil-dwelling bacteria that live deep within the Earth are highly-social creatures that have been in a process of gene exchange for eons.
The findings provide new insight into the "deep biosphere," which is believed to be equal in diversity to all the organisms inhabiting the land, sea and air combined, Dartmouth College reported. These observations could help scientists uncover secrets of Earth's early evolution.
In the past, researchers have suggested a "burial and isolation" scenario in which bacteria in these deep oil reserves are descendants of isolated bacterial communities present in surrounding sediments.
"Instead, our analysis supports a more complex 'colonization' view, where bacteria from subsurface and marine populations have been continuously migrating into the oil reservoirs and influencing their genetic composition since ancient times," said co-author Olga Zhaxybayeva, an assistant professor at Dartmouth.
To make their findings, the researchers analyzed 11 genomes of Thermotoga, which is an ancient lineage of heat-dwelling bacteria that exist in oil reserves in the North Sea and Japan, hot water vents on the ocean floor near the Kuril Islands, Italy and the Azores, an island chain west of Portugal. They also looked at Thermotoga community DNA from the environment of North America and Australia that has been stored in public databases.
The study results suggest a significant gene flow across all of the analyzed environments, indicating that the bacteria do not stay isolated in the oil reserves. This means the organisms most likely colonize and migrate, changing their genetic makeup.
"The pathway of the gene flow remains to be explained, but we hypothesize that a lot of the gene flow may happen within the subsurface," said co-author Camilla Nesbø, a researcher at Centre for Ecological and Evolutionary Synthesis at the University of Oslo.
The findings were published in a recent edition of the ISME Journal.
