How little can a cell get away with? Scientists have found a new clue in the DNA of marine plankton. Hidden in that genetic material was the genome of a previously unknown microorganism, named Candidatus Sukunaarchaeum mirabile — Sukunaarchaeum for short, named in honour of a small Japanese god.
Sukunaarchaeum belongs to the archaea, a group of single-celled organisms that are fundamentally different from bacteria. Its genome is less than half the size of the smallest archaeal genome previously known, and it contains just 189 protein-coding genes. That is remarkably few. Most living things carry far more instructions than that.
What makes the find interesting is not only what is there, but what is missing. Sukunaarchaeum has lost almost all the genes needed to produce its own nutrients and energy. On its own, it could not feed itself. That suggests it depends heavily on other organisms for the resources it needs to survive.
Yet it has kept something important. Despite its tiny genome, it still contains much of the machinery needed to copy its DNA and to use its genetic information to make proteins. That combination is unusual. Many organisms with very small genomes have given up some of that independence. Mitochondria and chloroplasts inside our cells, for example, were once free-living bacteria but now rely on their host cells for some of the machinery needed to copy and use genetic information. Sukunaarchaeum appears to have taken a different path: it gave up making its own food and energy, but kept the core machinery for reproducing its genetic information.
Professor Thorsten Allers of the University of Nottingham, a co-author of the study, put the question this way: the key to defining life is whether something can replicate itself, and whether it can do so autonomously. This discovery, he said, gives new clues about how simple a living cell can become while remaining capable of reproducing and maintaining its own genetic information.
There is a great deal the researchers do not yet know, and they say so plainly. The organism itself has not been directly observed, and its host has not been identified. It was found by analysing genetic material from individual marine microorganisms, not by growing it in a dish. Around a quarter of its genome consists of genes for unusually large membrane proteins whose functions are not yet known. Similar large membrane proteins are found in some parasitic archaea, which raises the possibility that Sukunaarchaeum lives as a parasite inside or alongside another organism — but that is a possibility to test, not a proven fact.
The work was carried out by an international team including researchers from the University of Nottingham and the University of Tsukuba in Japan, and published in the journal Current Biology. Related genetic sequences found in marine samples suggest Sukunaarchaeum is part of a much larger group of organisms that has so far gone largely unnoticed.
For GCSE biology, this is a useful reminder that "the smallest" and "the simplest" are not the same as "the least interesting". A cell is a set of jobs that must all get done: copying information, making proteins, getting energy, and keeping the whole system going. Sukunaarchaeum shows that some of those jobs can be handed to a neighbour, while the job of copying the genetic instructions stays in-house. Asking which jobs a cell keeps, and which it can afford to lose, is a better revision question than memorising a single number.
If biology sometimes feels like a long list of labels, a first lesson in biology can turn it into questions about how living things actually work — what a cell must do for itself, what it can borrow, and how scientists know what they do not know yet, with booster and mock-exam help in biology along the way. Book your first lesson
Sources:
- "Tiny marine microbe sheds new light on how little genetic machinery a cell needs to survive", Phys.org, 9 October 2026: https://phys.org/news/2026-10-tiny-marine-microbe-genetic-machinery.html
- "A hidden archaeal lineage with an ultra-reduced genome retaining only its replicative core", Current Biology (2026), DOI: 10.1016/j.cub.2026.09.042.