Scientists Discovered a New Creature That Exists Between Life and Not-Life

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6 hours ago

Here's what you'll learn when you read this story:
Viruses typically aren't considered 'alive,' as many core biological functions are outsourced to their hosts. But a newly discovered organism appears to straddle the line between virus and cell.
Like a virus, this new organism 'Sukunaarchaeum mirabile' outsources some functions to its host, but can still create its own ribosomes and RNA.
Its genome is also surprisingly small, and is roughly half the size (238,000 base pairs) of the next-smallest archaeal genome.
At first glance, creating a definition for 'life' seems somewhat straightforward. Sentient animals all the way down to single-celled organisms capable of reproduction are welcome on the tree of life, but there are other organisms that challenge this understanding, like viruses. Because virus don't grow, reproduce on their own, or make their own energy, they're typically excluded from definitions of life. But once a virus infects a host, it's immensely active, and can be responsible for world-altering events (see: Spanish flu, ebola, COVID-19, and so on).
However, life is complicated, and this controversial categorization of 'life' and 'not life' can have gray areas in which organisms appear to defy the expectations of both camps. Recently, scientists found a new member of this head-scratching cadre. In a new paper published on the bioRxiv server, researchers in Canada and Japan outlined how they identified a new cellular entity that appeared to straddle the typical definitions of a virality and cellular life.
Currently named 'Sukunaarchaeum mirabile' (after a deity in Japanese mythology known for its small stature), this entity contains the necessary genes to create its own ribosomes and messenger RNA—something your typical virus lacks. But like a virus, it offloads certain biological functions onto its host and it appears singularly obsessed with replicating 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 authors wrote. 'This suggests an unprecedented level of metabolic dependence on a host, a condition that challenges the functional distinctions between minimal cellular life and viruses.'
Led by Ryo Harada, a molecular biologist from Dalhousie University in Halifax, Nova Scotia, the team chanced upon this strange creature while studying the bacterial genome of the marine plankton Citharistes regius. Within the genomic data, Harada and his team found a loop of DNA that didn't match with any known species. They eventually determined that the organism belonged to the domain Archaea—a group associated with prokaryotic cells, but from which eukaryotic cells (i.e. you and me) ultimately descended a couple billion years ago.
Perhaps the most remarkable feature of Sukunaarchaeum is its extreme genome reduction, with only 238,000 base pairs of DNA. Viruses, as Live Science points out, can contain many hundreds of thousands more base pairs, and can even reach up into the millions. As for fellow archaea, the smallest known complete genome within this group stretches to 490,000 base pairs, meaning that Sukunaarchaeum contains less than half the number of base pairs posessed by even the smallest archaeal genome.
'The discovery of Sukunaarchaeum pushes the conventional boundaries of cellular life and highlights the vast unexplored biological novelty within microbial interactions,' the authors wrote. 'Further exploration of symbiotic systems may reveal even more extraordinary life forms, reshaping our understanding of cellular evolution.'
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