Japanese scientists discover microbes that survived over 100 million years on sea floor

The samples were recovered off the coast of Australia in a region where there is extremely low amounts of oxygen, energy, and nutrients.

Magnified image showing microbes revived from 101.5 million-year-old sediment | Image: JAMSTEC

Bengaluru: Microbial ecologists have managed to revive microbes that have been buried under the sea floor for over 100 million years. The microbes were still alive, and when brought back to the lab and given food, began to multiply. 

The microbial species survive on oxygen and the researchers state that they survived on the little bit of gas that is diffused from the surface of the ocean all the way to the sea floor. There was no other identifiable source of food or energy for the bacteria. 

The discovery points to the resilience of microbial life, which can survive on oxygen in minimal quantities, with low energy and food supply. It also has broader implications for our narrow search for extraterrestrial microbial life and habitability on other planets. 

The study was published in the journal Nature Communications Tuesday. It was conducted by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC), the URI Graduate School of Oceanography, US, the National Institute of Advanced Industrial Science and Technology, the Kochi University (Japan) and Marine Works Japan.

Discovery on 10-year-old samples

The discovery was made on samples extracted from a drilling expedition 10 years ago to the South Pacific Gyre, an area where ocean currents flowing in different directions intersect. The site is situated to the east of Australia and is considered to be “dead” — almost completely lacking in nutrients needed for life to survive. 

The team dug up and extracted clay and sediment cores from nearly 5700m or 19,000 feet below sea level, and about 100m into the sea floor. The samples were placed in glass containers and were fed compounds like ammonium, which can detect living microbes. 

Seabed typically consists of organic matter but around Australia, New Zealand, and Oceania, there is much less organic matter as there is not a lot of life on the surface. The sea floor is primarily volcanic rock from the nearby land structures, and also consists of dust from outer space. 

“Our main question was whether life could exist in such a nutrient-limited environment or if this was a lifeless zone,” said the paper’s lead author Yuki Morono, senior scientist at JAMSTEC, in an accompanying release. “And we wanted to know how long the microbes could sustain their life in a near-absence of food.”

‘Newly-discovered microbes are aerobic’

The scientists found that while there are typically 1,00,000 cells per cubic centimetre of sediment from the sea floor, these samples contain only about 1,000 bacteria in the same amount of volume. 

Using DNA sequencing, the team also confirmed that the microbes were aerobic, and fell into eight groups of bacteria commonly found in saltwater in other parts of the world. The samples confirmed the presence of minimal oxygen and organic matter.

The team is not sure how the bacteria survived all this while as they did not form spores, the forms bacteria take when they want to hibernate during unfavourable environmental conditions where they cannot feed or multiply. The team is also unsure whether the bacteria have been multiplying, albeit slowly, for millions of years.

For up to 557 days, efforts were taken to extract tiny bits of samples from the existing ones and isolate living matter from it. After isolation, the bacteria were incubated and fed to see if they were capable of growing and multiplying.

 “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,” said Morono.