A New Organism With a Tiny Genome Lives Like a Vampire

Researchers led by scientists from Dalhousie University discovered Candidatus Sukunaarchaeum mirabile, an archaea with the smallest genome ever recorded for a cellular organism, found incidentally while studying marine plankton near Shimoda, Japan. Its genome is so stripped down it has lost nearly all metabolic genes, yet unlike a virus it still retains its own machinery to copy DNA and build proteins. The discovery raises questions about whether it is a parasite or symbiont, and researchers now believe it represents a wider, previously unnoticed group they call the Sukuna clade. The finding blurs the boundary between viruses and living cells and offers a window into how free-living microbes can evolve into organelles.

• Its genome lacks virtually all standard metabolic pathways, so it cannot make its own nutrients, energy, or cell components [01:23]
• It was found incidentally while researchers collected single-cell marine plankton (Citeristes regius) off Shimoda, Japan, not while searching for record-breaking microbes [02:17]
• The organism's circular genome is about 238,000 base pairs with 189-190 protein-coding genes [02:47]
• For comparison, E. coli has 4-5 million base pairs while the previous smallest known bacterial genome was about 500,000 base pairs [02:59]