Revival of marine microbes inactive for over 100 million years questions limits of Earth's habitable space: Study

About 99% of the microbes trapped in sediment deposited 101.5 million years ago were still alive and were ready to eat and multiply, say experts involved in the study


                            Revival of marine microbes inactive for over 100 million years questions limits of Earth's habitable space: Study
Researchers studying samples gathered from the South Pacific Gyre. (Photo: ODP JRSO)

Sea-dwelling microbes that stayed inactive for over 100-million-year-old have been brought back to life by scientists in a new study. These microbes occupied an inhospitable region or an ocean desert, where nutrients are hard to come by. 

Scientists discovered microbes trapped in sediments. They were buried about 245 feet under the seafloor of the South Pacific Gyre, also called the ocean's desert. It sits between Australia and South America.  Marine sediments are deposits of rock materials carried by the wind from the land to the sea or are remains of marine organisms or volcanic materials or meteorites that landed from space. These sediments are home to a range of microbial populations.

“Our main question was whether life could exist in such a nutrient-limited environment or if this was a lifeless zone,” said the study’s lead author Yuki Morono, senior scientist at Japan Agency for Marine-Earth Science and Technology (JAMSTEC), said in a statement. “And we wanted to know how long the microbes could sustain their life in a near-absence of food.”

The researchers then tried to grow the microbes in an incubator by feeding them for 557 days. They were stunned to see that they were not fossils, but live bacteria that woke up from hibernation after eons to multiply. “At first, I was skeptical, but we found that up to 99.1% of the microbes in sediment deposited 101.5 million years ago were still alive and were ready to eat,” Morono added.  

Magnified image showing microbes revived from 101.5 million-year-old sediment. (JAMSTEC)

“It is surprising and biologically challenging that a large fraction of microbes could be revived from a very long time of burial or entrapment in extremely low nutrient or energy conditions,” Morono. Finding out the life on sediments had no limits is the most exciting part of the study, Steven D’Hondt, the co-author of the study from the University of Rhode Island pointed out. "In the oldest sediment we’ve drilled, with the least amount of food, there are still living organisms, and they can wake up, grow, and multiply," he added.

The study opens up the possibility of studying how ancient organisms evolved sub-seafloor. Monroe explained that life below seabed moves at a slower rate, meaning mutations that drive evolution could be slow too. “This study shows that subseafloor is an excellent location to explore the limits of life on Earth," he explained.

They also want to investigate how these microbes pulled off this feat. "We now know there is no age limit (to organisms), but there should be the end of the biosphere in somewhere of the subseafloor," he said. "We want to see the extent of the habitable space in our Earth and know the life-limiting condition in detail," Morono told CNN.

Commenting on the study, Yohey Suzuki, an associate professor in the department of earth and planetary science at The University of Tokyo told CNN that the findings hold global importance "but is difficult to extrapolate to the other (ocean sediments), because sediments are complex and vary from one site to another." He wasn't involved in the study.

The study is published in Nature Communications.

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