Scientists and philosophers have long grappled with defining life. A significant breakthrough occurred in 2025 with the discovery of Candidatus Sukunaarchaeum mirabile, an archaeon with an exceptionally small genome.
This discovery, led by Ryo Harada at Dalhousie University, was made while studying the DNA of plankton species Citharistes regius. Researchers identified an unusual DNA loop, indicating a biological entity unlike any previously known.
Phylogenetically, Candidatus Sukunaarchaeum mirabile belongs to the archaea group, single-celled microorganisms distinct from bacteria and eukaryotes. However, its characteristics resemble viruses. Its genome, with only 238,000 base pairs, is the smallest ever observed in an archaeon.
This minimal genome primarily codes for DNA replication, transcription, and translation mechanisms, lacking classic metabolic pathways. This structure suggests extreme metabolic dependence on a host, blurring the lines between minimal cellular life and viruses.
Researchers noted that "Candidatus Sukunaarchaeum mirabile could represent the cellular entity closest to a viral existence strategy." This specialization challenges our fundamental understanding of the minimum requirements for cellular life.
This discovery underscores the complexity of life and the need to re-evaluate traditional definitions. It also paves the way for future research on symbiotic interactions and the evolutionary strategies of microorganisms.
Note that this study is a pre-publication and has not yet been peer-reviewed, requiring careful interpretation of the results. This advancement reminds us that the boundaries of biology are blurred, and discoveries like this can transform our understanding of life.