Meet the organism which hangs somewhere between life and death

Time of India

03-07-2025

Scientists have discovered Sukunaarchaeum mirabile, a unique archaeon residing within marine plankton, challenging traditional definitions of life. This microbe possesses a stripped-down genome, enabling protein production but lacking metabolic pathways, blurring the lines between cellular life and viruses. Its discovery prompts a reevaluation of life's boundaries and evolutionary origins.
Scientists have long debated what truly counts as 'alive.' On one side of the spectrum lie conscious animals and self-replicating single-celled organisms, whereas on the other side are viruses, which are the biological entities that can only function once they hijack a host.
Viruses don't grow, reproduce independently, or generate their own energy, so they're usually excluded from the tree of life. But life's boundaries aren't always clear-cut. New discoveries are challenging the binary notion of 'living' versus 'non-living.'
A recently discovered organism is a surprising microbe that shares traits with both viruses and cellular life. It can construct its own ribosomes and messenger RNA, yet it lacks most metabolic pathways and relies heavily on its host. So this brings us to some unanswered questions like, what defines life? Where do we draw the line? And could this microbe represent a missing link in evolutionary biology?
Researchers led by Ryo Harada at Dalhousie University uncovered an unusual archaeal organism within the marine plankton Citharistes regius.
While studying the plankton's bacterial genome, they discovered a circular DNA fragment that didn't match any known species. Detailed analysis showed the scientists that it belongs to the Archaea domain and is provisionally named Sukunaarchaeum mirabile, inspired by a tiny Japanese deity.
This virus can produce its own proteins!
Surprisingly, its genome is just 2,38,000 base pairs, which is about half the size of the smallest previously known archaeal genome, which was 490 kbp.
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'Its genome is profoundly stripped‑down, lacking virtually all recognizable metabolic pathways, and primarily encoding the machinery for its replicative core: DNA replication, transcription, and translation,' the team of researchers revealed in the study.
This minimal genome means an undefined metabolic dependence on its host.
Still, Sukunaarchaeum retains key machinery most viruses lack, like the genes for building ribosomes, transfer RNA, and messenger RNA.
Unlike viruses, which rely fully on host machinery, this archaeon can perform fundamental cellular processes. The team says, 'Sukunaarchaeum may represent the closest cellular entity discovered to date that approaches a viral strategy of existence'.
This virus belongs to an old branch of a family tree
Study
also reveals that the scientists found that Sukunaarchaeum mirabile belongs to a very old and unique branch of the Archaea family tree, which is so unique that it may come from a group of microbes that have never been observed before.
Even though researchers have done tons of environmental DNA sequencing over the years, this strange little organism stayed hidden inside plankton DNA until now.
Its tiny, simplified genome is making scientists rethink how we define life. Sukunaarchaeum blurs the line between the smallest living cells and complex viruses. It can copy its own DNA and make proteins, things that viruses usually can't do on their own, but it still relies completely on its host to survive because it can't produce its own energy.
In short, this organism sits in a gray area between life as we know it and the strange, parasitic world of viruses.