Named Sukunaarchaeum mirabile, this new entity, found within the domain Archaea, challenges conventional understandings of biology by exhibiting both viral and cellular characteristics. Its genome is remarkably small, even by the standards of other microorganisms, yet it retains functions typically seen in living cells.
In biology, the question of what constitutes “life” is far from simple. Traditionally, viruses have been excluded from this category because they cannot replicate or produce energy without a host. However, Sukunaarchaeum mirabile complicates this binary definition. While it relies on a host for certain biological functions, it also possesses the ability to produce its own ribosomes and messenger RNA, which viruses typically lack. This dual nature makes it an intriguing subject for researchers aiming to refine the boundaries of life.
A New Discovery At The Edge Of Life
The discovery of Sukunaarchaeum mirabile came about during a study of marine plankton’s bacterial genome. According to researchers from Dalhousie University and Japan’s RIKEN Institute, they stumbled upon a loop of DNA in the genome of Citharistes regius, a type of marine plankton, that didn’t match any known species.
Upon further analysis, the team identified this DNA as belonging to a previously unknown form of life, which they later named Sukunaarchaeum. This organism belongs to the domain Archaea, a group of single-celled organisms that are distinct from bacteria but are related to the cells that make up more complex life forms, including humans.
Despite its complex lineage, Sukunaarchaeum displays some features typical of viruses, particularly in its reduced metabolic capabilities. It has a remarkably small genome—only 238,000 base pairs, which is less than half the size of the smallest known archaeal genome. This extreme reduction suggests that the organism relies heavily on its host for survival, but it still retains just enough biological machinery to function on its own to some degree, reports Popular Mechanics.
Straddling The Line Between Virus And Cell
What makes Sukunaarchaeum particularly fascinating is its hybrid nature. Like viruses, it offloads many key biological functions to its host, including most metabolic processes. However, unlike viruses, Sukunaarchaeum can independently create its own ribosomes, which are essential for protein production, as well as messenger RNA (mRNA), which carries genetic information for protein synthesis. These features are typically seen in living organisms, not viruses, which rely entirely on their hosts for these processes.
In their research, pubslished in bioRxiv, the team led by molecular biologist Ryo Harada noted that Sukunaarchaeum’s genome is primarily focused on replication. It encodes machinery for DNA replication, transcription, and translation, but lacks most of the metabolic pathways seen in other forms of cellular life. According to the researchers, this unique balance of self-reliance and dependence on a host challenges traditional distinctions between cellular life and viruses.
What This Discovery Means For Life’s Definition
The discovery of Sukunaarchaeum forces a rethinking of the criteria used to define life. If organisms like this exist, then the conventional boundary between viruses and cellular life becomes blurry. Traditionally, life has been defined by the ability to grow, reproduce, and produce energy independently. Viruses, which cannot do any of these things on their own, have been excluded from this definition. However, Sukunaarchaeum shows that life might not be as simple as a clear-cut definition.
According to the team, the organism’s genome reduction and its symbiotic relationship with its host could represent an evolutionary step toward simpler life forms. The research team believes that this discovery could open up new avenues for exploring the diversity of life at the microbial level. If more organisms like Sukunaarchaeum exist, they could offer new insights into the early evolution of life on Earth and perhaps even on other planets.