Scientists uncover a microbe challenging the definition of ‘Life’; a discovery that could rewrite biology textbooks

A clear, simple definition of life has always been hard to pin down and remains elusive. Most biology lessons say living things must grow, produce energy, and reproduce on their own. But viruses don’t fit this idea; they only become active inside another organism and remain dormant otherwise.

Researchers led by Ryo Harada from Dalhousie University found a strange new organism named Sukunaarchaeum mirabile. It was discovered hidden in DNA taken from plankton off the coast of Japan. This tiny microbe is unlike anything seen before because it has some features of living cells but also acts like a virus in many ways.

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Unlike viruses, Sukunaarchaeum has genes to make its own ribosomes and messenger RNA, essential for protein production. But it relies heavily on its host cell for nearly everything else it needs to survive.

The smallest genome for a cellular organism

This microbe’s genome is extremely small, just 238,000 base pairs long, about the size of a medium magazine article. For comparison, another tiny archaeon, Nanoarchaeum equitans, has about twice as many base pairs, according to an Earth.com article. Viruses can be smaller or bigger, but never carry all the genes needed to make proteins.

Harada’s team describes Sukunaarchaeum as “a cellular entity retaining only its replicative core,” meaning it keeps only the basic genetic tools to copy itself.

What makes Sukunaarchaeum unique?

Its genome lacks almost all the genes for metabolism, the chemical processes that normally allow cells to make energy and grow. Instead, it mainly carries genes for DNA replication, transcription, and translation, which are more like a virus’s instruction set.

Despite this, Sukunaarchaeum is firmly part of the Archaea domain, one of the three main branches of life, and may represent a completely new group of organisms.

How was it found?

Scientists found Sukunaarchaeum’s DNA while studying a type of plankton called Citharistes regius. They noticed a loop of DNA that didn’t match any known species. Many marine organisms live closely with other microbes, sometimes even hosting them inside their cells. Sukunaarchaeum seems to take this relationship to the extreme by losing genes it can depend on its host to provide.

Why does this matter?

Earth.com explains that this discovery challenges how we define life. Since Sukunaarchaeum keeps ribosomal genes, it meets the standard test for being cellular.

But its tiny metabolism means it can’t survive independently like normal cells. This pushes the idea that life exists on a spectrum, not as a simple yes-or-no category.

This matters for many reasons, including how governments decide what is “alive” when making health policies or protecting the planet from contamination by space missions. It also offers clues for synthetic biologists creating minimal cells with just the essential genes.