In the ever-expanding universe of microscopic life, scientists have uncovered something that might force us to redraw the boundaries of what counts as “alive.”
Meet Sukunaarchaeum mirabile, a tiny cellular oddity recently discovered by researchers in Canada and Japan, according to a new paper published on thebioRxiv server. It’s not quite a virus, and it’s not fully a living cell either, but it carries traits of both.
Named after a Japanese deity famed for its small size, Sukunaarchaeum sports one of the smallest genomes ever recorded—just 238,000 base pairs, less than half that of the previous smallest-known archaeal genome.
And while viruses are typically excluded from the tree of life due to their reliance on host cells for key functions, this organism complicates that definition in a big way.
Like a virus, Sukunaarchaeum relies on a host to carry out many of its biological tasks. But unlike a virus, it’s capable of building its own ribosomes and messenger RNA. These are the basic building blocks that enable an organism to translate genetic code into protein, which is something viruses can’t do on their own.
Its stripped-down genome reveals an obsessive focus on replication. It contains little else besides the machinery needed to copy itself.
“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 researchers wrote.
This means it leans heavily on its host for everything from energy to nutrients.
The discovery happened almost by accident.
Molecular biologist Ryo Harada and his team at Dalhousie University were examining the DNA of a marine plankton species when they found a strand of genetic material that didn’t match any known organism. After digging deeper, they identified it as part of the Archaea domain—a group of ancient microbes from which modern complex cells likely evolved.
If Sukunaarchaeum proves anything, it’s that nature doesn’t follow strict definitions. In fact, this discovery could fundamentally reshape how we think about cellular evolution and the blurry line between life and not-life.
Related: Doctors Found a New Blood Type and It Changes What We Thought We Knew
Scientists Just Discovered a Creature That Breaks the Rules of Life first appeared on Men's Journal on Jul 1, 2025
