A cell so minimal that it challenges definitions of life
51 comments
·November 26, 2025stevenjgarner
sigmoid10
You could argue the same way for a lot of parasite species, many of which are ridiculously more complex. Is a complex multicellular organism (an animal even) not alive because it needs to get some component needed for its reproduction from another species? If you get hung on such specific components, where do you draw the line?
pretzellogician
Very impressive! To be clear, this is not the smallest known bacterial genome; only the smallest known archaeal bacterial genome, at 238k base pairs.
In the article they mention C. ruddii, with a smaller 159k base pair genome.
But according to wikipedia, it seems N. deltocephalinicola, at 112k base pairs, may be the smallest known bacterial genome. https://en.wikipedia.org/wiki/Nasuia_deltocephalinicola
oersted
That’s interesting. The main difference seems to be that those other tiny organisms only encode how to produce some metabolic products for the host but cannot reproduce independently, so they are quite close to being organelles. Instead, this new one pretty much only produces the proteins it needs to reproduce and nothing for the host.
The new one with 238 kbp:
> Sukunaarchaeum encodes the barest minimum of proteins for its own replication, and that’s about all. Most strangely, its genome is missing any hints of the genes required to process and build molecules, outside of those needed to reproduce.
Referencing the 159 kbp one:
> However, these and other super-small bacteria have metabolic genes to produce nutrients, such as amino acids and vitamins, for their hosts. Instead, their genome has cast off much of their ability to reproduce on their own.
flobosg
A nitpick: Although similar in some aspects, archaea are not bacteria; they are classified under their own phylogenetic domain.
api
Still far, far too complex to occur "randomly," which is fascinating. The odds of 112k bases arranging in any meaningful way by chance within a membrane are the kind of thing you wouldn't get if you ran a trillion trillion trillion universes.
There's many hypotheses, basically all different variations on "soup of organic compounds forming complex catalytic cycles that eventually result in the soup producing more similar soup, at which point it begins to be subject to differential selection." It's a reasonable idea but where did this happen, and do the conditions still exist? If we went to that place would it still be happening?
There's reason to believe the answer would be no because modern lifeforms would probably find this goo nutritious. So life may have chemically pulled up the ladder from itself once it formed.
This of course assumes no to more fanciful options: panspermia that pushes the origin back to the beginning of the cosmos and gives you more billions of years, creation by a God or some other kind of supernatural or extra-dimensional entity, etc.
smallmancontrov
1. Autocatalytic RNAse reaction networks -- "soup producing more soup" -- are easily replicated in the lab, subject to Darwinean processes, and are at the center of ongoing study. "0 to Darwin" is now easy and God of the Gaps must retreat once again.
2. Spores hitchhiking on impact ejecta sounds exotic until you realize that anywhere life is present at all spores will be everywhere and extremely sturdy. That desktop wallpaper you have of planets crashing together and kicking off an epic debris cloud? Everything not molten is full of spores.
3. Religious explanations are not in the same universe of seriousness as 1 and 2. Opening with a religious talking point and closing with a false equivalence is mega sus.
bavell
Would love to see some sources for #1. #2 sounds plausible but speculative?
alonmower
If you’re interested in this area I highly recommend “The Votal Question” by Nick Lane if you haven’t read it.
The TLDR of his theory is that life originated in alkaline hydrothermal vents on the ocean floor, where natural energy gradients could have driven primitive metabolic reactions before the development of DNA.
Book goes into a lot of layperson-accessible detail.
ferfumarma
> Still far, far too complex to occur "randomly," which is fascinating
Why spend time making this point? Nobody believes that this occurred randomly: it occurred via evolution.
The mutations are a random part of evolution, but the process overall is not random at all - no more so than your immune system (which randomly generates antibodies, then selects against those that target innate epitopes), or stable diffusion (which starts with random noise, then marches up a gradient toward a known target).
It is the selection step that makes similar processes non-random, because a random selection step would just be noise.
andrewflnr
This is cool but doesn't say much about the definition of life IMO. They're obligate parasites. This isn't a new category. They're still eating stuff from their host (probably, given the caveat later in the article), and still using it to replicate, it's just a more limited diet.
flobosg
> They're still eating stuff from their host
They aren’t. Apart from DNA replication, transcription, and translation, their genome lacks elements encoding for even the most simple metabolic pathways.
subroutine
Impressive. However, still a-ways to go before its as degenerate as viruses like SARS-CoV-2 (which have an order of magnitude fewer base-pairs)
codedokode
> the bacterium Carsonella ruddii, which lives as a symbiont within the guts of sap-feeding insects, has an even smaller genome than Sukunaarchaeum, at around 159,000 base pairs
159 000 base pairs is ~320 Kbit, or 40 KBytes. I wonder, if that is the minimum size of a cell firmware. Also, if the cell is that simple, can we study it exhaustively and completely? Like, decipher every base pair in DNA, and determine what it is responsible for. And make an interactive website for that.
ErroneousBosh
This is the biological equivalent of sectorlisp.
empiricus
I think the genome might be mostly just the "config file". So the cell already contains most of the information and mechanisms needed for the organism. The genome is config flags and some more detailed settings that turn things on and off in the cell, at specific times in the life of the organism. From this point of view, the discussion about how many pairs/bytes of information are in the genome is misleading. Similar analogy: I can write a hello world program, which displays hello world on the screen. But the screen is 4k, the windows background is also visible, so the hardware and OS are 6-8 orders of magnitude more complex than the puny program, and the output is then much more complex than the puny program.
djoldman
From the paper: https://www.biorxiv.org/content/10.1101/2025.05.02.651781v1
> ... we report the discovery of Candidatus Sukunaarchaeum mirabile, a novel archaeon with an unprecedentedly small genome of only 238 kbp —less than half the size of the smallest previously known archaeal genome— from a dinoflagellate-associated microbial community.
russdill
For comparison, the smallest bacteria genome, nasuia deltocephalinicola, is 139 kbp.
tete
Talking about tiny cells and staring at a tube with liquid. Made me chuckle.
flobosg
See also: “Microbe with bizarrely tiny genome may be evolving into a virus” – https://www.science.org/content/article/microbe-bizarrely-ti...
HarHarVeryFunny
Maybe devolving would be a better term if that's the case
smollOrg
> According to the shocked researchers
What is this, some content creator run Biohacker Lab in some basement on Microflix premises?
Ominous voice: the tiny cell withdrew into the cracks of existence and saved it's entire code to be in the lines between, the Singular Point which was neither a fraction of space, nor a unit of time, hidden in the void of Chututululu's (33rd degree cousin of Cthulhu) dreams, written in the unspeakable language of the subtext of the book of neither life nor death, that nobody would decipher until the time was right AND GODZILLA GETS TO WALK THE EARTH AGAIN.
IAmBroom
They were shocked. It is shocking.
moffkalast
Well tell them to quit playing with the stun gun.
null
Isn't replication the single most important act of metabolism for an organism? I am trying to reconcile their ""lost genes include those central to cell metabolism, meaning it can neither process nutrients nor grow on its own" with their "The organism’s “replicative core” — the genetic components needed to reproduce itself — remains, making up more than half of its genome".
Replication (making DNA, RNA, and proteins, and ultimately dividing) is a highly energy-intensive and material-intensive process. What appears to be lost by Sukunaarchaeum are the genes to build basic building blocks (amino acids, vitamins, nucleotides) from scratch. It cannot find a sugar molecule and break it down for energy (it can "neither process nutrients nor grow on its own"). Yet it can take pre-made energy and building blocks and assemble them into a new organism.
What is the exact line between the host's metabolic contribution and the archaeon's replicative assembly? How "finished" are the raw materials that the host provides, and how does the archaeon's extremely reduced genome still manage the subsequent steps of self-replication?