Washington: In a significant revelation that may help us understand about life's early evolution on Earth and contribute to the search for life on Mars, a study has shown that microbes living under the vast reserves of oil deep underground are social creatures.
These microbes, that are the oldest form of life on earth, are roughly equal in number and diversity to all the microbes inhabiting the surface's land, water and air.
Oil reservoirs are scattered deep inside the Earth like far-flung islands in the ocean, so their inhabitants may be expected to be very different.
Earlier theories supported a "burial and isolation" case where bacteria in oil reservoirs were thought to be descendants of isolated bacterial communities buried with sediments that over time became oil reservoirs.
"Instead, our analysis supports a more complex 'colonisation' view, where bacteria from sub-surface 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 College, in the US.
Microorganisms are the oldest form of life on Earth and continue to play a crucial role in the planet's ecosystem.
Those bacteria dwelling underground live not off sunlight's energy but the Earth's inner heat, chemicals and nutrients.
For the study, researchers analysed 11 genomes of Thermotoga, an ancient lineage of heat-loving bacteria. They also analysed Thermotoga community DNA from North America and Australia that are available in public databases.
An extensive gene flow across all the sampled environments was found suggesting that the bacteria did not stay isolated in the oil reservoirs.
They long migrated to and colonised the reservoirs and contributed to their genetic make-up, the study showed.
"The pathway of the gene flow remains to be explained, but we hypothesise that a lot of the gene flow may happen within the subsurface," explained Camilla Nesbo, researcher at the Centre for Ecological and Evolutionary Synthesis at University of Oslo.
The authors' previous research showed that Thermotoga and its close relatives have exchanged genome with two other distant groups of bacteria.
The study appeared in the ISME Journal.