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The Rigakubu News

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The Rigakubu News
The Rigakubu News, January 2025.

The Frontiers of Research for Undergraduatesy >

Uncovering the origins of life through 2 billion year old microorganisms

Yohei Suzuki ( Associate Professor, Department of Earth and Planetary Science)

 

We have succeeded in collecting microorganisms that appear to be alive from a stratum 2 billion years ago,
significantly surpassing the previous record of 100 million years ago.
If these microorganisms have been enclosed in rocks for 2 billion years and have hardly evolved,
it will be possible to examine the genes of ancient creatures.
The genetic information is expected to provide clues to solving the mystery of the "origin of life.

How did life originate? The "origin of life," a theme that is both familiar and grandiose, has been studied mainly through three approaches.

The first approach is to search for traces of life in the strata of the earth's earliest strata, traces of which have been found in the strata of 4 billion years ago. The second approach is based on "chemical evolution. Chemical evolution" refers to the process by which complex organic substances such as amino acids and proteins are gradually formed from simple chemical substances, leading to the emergence of life. The third approach is from the viewpoint of "biological evolution. Ten years ago, only a single gene could be used to create a phylogenetic tree of all life, but today, more than 100 genes can be used to create a phylogenetic tree of all life.

Based on the latest phylogenetic tree of all life, microorganisms living deep underground were found to be closely related to the common ancestor. These microorganisms inhabit the deep subsurface all over the world, and their genomes are almost identical when compared on a global scale, suggesting that they have not evolved on a 100 million year scale. Therefore, deep underground is beginning to be recognized as a place where organisms do not evolve, unlike above ground, and also as an important habitat for primitive microorganisms that are closely related to the common ancestor.

In some metal mines, ore from strata older than 2.5 billion years is mined from tunnels more than 2 kilometers underground. Groundwater extracted from mine shafts in Canada and South Africa has been reported to have been trapped in deep strata for more than a billion years. This fact confirms the existence of an ultra-enclosed space where water, let alone living organisms, cannot enter or exit on a billion-year scale.

Our team has focused on a platinum-rich formation in South Africa that was formed 2 billion years ago, called the Bushveld Complex. It consists of ultrabasic rocks (composed mainly of iron- and magnesium-rich olivine and pyroxene) similar to mantle materials, which are considered important in relation to the birth of life. Because the rocks were obtained by drilling from the surface, we had to carefully examine them for contamination by terrestrial organisms that could penetrate inside the rocks. It was also necessary to develop a technique to visualize creatures so small that they could not be seen by the naked eye within the rocks. We were the first in the world to successfully overcome these two challenges.

Work at an excavation site in a platinum mine (left), a crack in a rock core where microorganisms were discovered, and a fluorescence microscope image of dense microorganisms (right).

What was revealed was the appearance of life inside the rock 2 billion years ago. Microorganisms are densely packed in the crevices of the rocks, which are clogged with a material called clay. This means that contaminating microorganisms cannot enter, and in turn, the microorganisms living in the crevices cannot move out.

The key point of future research is to clarify how closely related the microorganisms living in this formation are to the common ancestor and how much they have not evolved. It is hoped that the approach of "biological evolution" will lead us closer to the elucidation of the "origin of life.

The results of this research were published in Y. Suzuki et al. Microbial Ecology. 87, 116 (2024).

 

(Press release on October 2, 2024)