Life’s evil twins—mirror cells—could doom Earth if scientists don’t stop themNEWS | 26 January 2026Let’s say it’s 2036, and scientists are working on a new class of drugs. These medications are mirror-image versions of the molecules your body uses to fight disease. Their big advantage is that reverse compounds last longer in the body because destructive enzymes don’t recognize them and rip them apart. Yet the compounds are still effective against invading microbes. Clinical trials have been promising, and the team is eager to scale up production.
The researchers turn to engineered mirror bacteria—single cells made of reversed molecules—for the job. Bacterial factories aren’t a far-fetched idea. Today, for instance, pharmaceutical companies use bacteria to manufacture synthetic insulin for diabetics. Curious about whether mirror cells could be used in a similar way, the scientists experiment on a mirrored version of the common bacterium Escherichia coli.
Unfortunately, a researcher with a small cut on her thumb from dry skin forgets to put on her gloves and touches a surface contaminated with just a few of these cells. The bacteria get into her blood.
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Her immune cells, which usually kill off intruders, don’t recognize the mirror proteins on the novel bacteria and fail to react. The mirror microbes multiply and spread within her. Defensive antibodies never appear. After a few days at home, the scientist falls gravely ill. She’s taken to a hospital, where she’s loaded with antibiotics that can’t make up for the massive failures of her immune system. Three days later she dies.
But while in her house, she had already spread the bacteria around. Her cat carries some into the garden, where they grow in the soil. Worms and insects become infected and transmit the mirror microbes throughout the neighborhood. Her children bring the bacteria to school. More and more people fall ill and begin to die. New outbreaks start in other locations as people and animals travel. A process of exponential and irreversible growth has begun—one that could quickly cover the world.
The scenario sounds like a sci-fi movie. But it is much closer to reality.
Scientists have been making rapid progress on technologies that could make it possible to build mirror organisms in the coming decades. Already biochemists can create increasingly complex mirror molecules, including enzymes that build mirror RNA. In the near future, similar enzymes could make reversed DNA. At the same time, synthetic biologists are getting closer to building regular bacterial cells from scratch. If progress in these two fields converges, it will be possible to build mirror bacteria.
A little more than a year ago I and 37 of my colleagues published a warning about this potential catastrophe in Science, insisting on a halt to this work. But how do we stop or control research that can take place in dozens of laboratories in many countries all over the world? This is the story of that challenge—and our plan to prevent a terrible future.
The first glimpse of that future emerged in 1848, when a young Louis Pasteur took the podium at the French Academy of Sciences in Paris and announced a remarkable discovery. Pasteur had been looking closely at the crystals of an acid found in wine. These compounds could take one of two forms that, despite being chemically identical—made of the same chemical building blocks and bonds—had opposite configurations. Hold your two hands in front of you, palms up. Their components are equivalent (four fingers, a thumb, a palm, etcetera), but they point in two different directions.
It turns out that almost all the basic molecules of life can exhibit this intriguing duality, as if one is the mirror image of the other. This property is called chirality. Other molecules, in contrast, are perfectly symmetrical; those are called achiral. Most large biological molecules are chiral, like our hands. No matter how you turn and twist molecules that are chiral opposites, you cannot make them overlap completely. But if a large group of people stacked their identically chiral left hands on top of one another, in the same orientation, the hands would overlap. Groups of chiral molecules are usually referred to as “left-handed” or “right-handed,” depending on which orientation they have in common. All life on Earth—everything that has descended from our last primordial common ancestor, which lived four billion years ago—builds its classes of molecules from only one of these two possible forms. Nineteen of the 20 amino acids that make up proteins are left-handed, for instance, whereas DNA and RNA twist to the right.
These microbes would have a strong claim to be the most dangerous biological threat ever known.
But there’s no reason that mirrored versions of these building blocks can’t exist, and indeed, many are found in nature. Although almost all amino acids are left-handed, right-handed amino acids D-alanine, D-methionine and D-leucine (the D prefix comes from the Latin dextro, meaning “right”) appear in bacterial cell walls. Some others are being made in labs: right-handed versions of short amino acid chains are being synthesized as candidates for new drugs. As noted, their unusual orientation renders them resistant to enzymes that would otherwise latch on and destroy them. Astrobiologists have long thought life could have conceivably evolved in the opposite configuration—and, intriguingly, both left- and right-handed amino acids were found on the asteroid Bennu in approximately equal quantities.
Scientists have already made a few mirror components. In 1993 researchers then at Johns Hopkins University reported making a right-handed version of the typically left-handed protein rubredoxin. More incremental work of this type has continued in the ensuing decades. Then, in 2022, other researchers announced they had built parts of a mirror-image enzyme that made a reverse RNA molecule. RNA is the essential template for most proteins, and it also plays crucial roles in numerous other processes essential to life. This engineering feat brought us much closer to making mirror components and assembling them into a functional mirror bacterial cell.
But it would be a killer mirror. Microbes like these would have a strong claim to be the most dangerous biological threat we’ve ever known. They could survive and grow on a range of naturally occurring nutrients in the environment. Yet they would probably be resistant to the many predators—viruses and protozoans—that keep populations of bacteria in check in the natural world. Such predators, after being selected during millions of years of evolution to recognize one protein shape, would not detect the opposite configuration. For the same reason, mirror cells could evade many parts of the immune system, causing infections likely to be fatal in people, animals and plants. They could spread and evolve rapidly in the environment, acquiring mutations that would enable them to grow on other nutrients, which would make them even more dangerous. And they could be impossible to eradicate, becoming a perennial source of infections that no human, plant or animal could fight.
When I first heard of this idea, about two years ago, I thought it must be science fiction. I figured the initially constructed mirror organism would be too fragile to live and reproduce. The closest things we have to synthetic life today are flimsy and delicate: test-tube-bound, not suitable for natural ecosystems and environmental pressures. Surely the mirror versions of artificial life-forms would be doubly so. For instance, what would they eat? Most of the molecular food sources that power life on Earth are chiral, too—wouldn’t mirror bacteria need similarly oriented nutrients when they first escaped into the wild and starve if those nutrients didn’t exist?
When some colleagues and I started to look into it, I learned that we were dangerously wrong. There are indeed many nutrients that mirror bacteria could digest, including many achiral symmetrical ones. Experiments have shown that populations of some natural bacteria, such as E. coli, can grow on only achiral nutrients, and mirror bacteria would be able to do the same.
Nor would a mirror organism necessarily be as fragile as the highly modified, close-to-synthetic cells we have today—cells like the ones my colleague John Glass’s team at the J. Craig Venter Institute has constructed with a minimal number of genes or organisms like those that George Church’s group at Harvard University has “recoded” with slight alterations in their DNA. These are the product of thousands of engineering steps that make them much more delicate than bacteria that thrive in the environment. In contrast, mirror bacteria could be identical to robust natural bacteria in all ways but one, confounding our intuitions about the fitness of engineered life outside the lab.
Brown Bird Design; Source: Technical Report on Mirror Bacteria: Feasibility and Risks, by Katarzyna P. Adamala et al.; December 2024 (primary reference for graphic)
What would happen if mirror bacteria got even a tiny foothold in the natural environment? The result could look a lot like the work of my mentor, evolutionary biologist Richard Lenski of Michigan State University. He has conducted experiments in which a dozen cultures of naturally chiral lab-grown E. coli are given a fresh glucose meal every morning. He found that even genetically identical microbes would quickly evolve and diversify, becoming distinct communities.
My work with infectious bacteria has shown that permanent and meaningful diversification may require only hundreds of generations. Mirror bacteria could evolve in the same way. It wouldn’t be a one-and-done event: you’d create a second tree of life that would trace its own evolutionary paths through diverse ecosystems, finding niches wherever it could. An accidental release could cross an irreversible threshold.
People would be on the wrong side of that passage. Ordinarily, the trillions of bacteria living in our gut provide an early defense against normal-chirality pathogens: some produce antibacterial molecules that directly inhibit or kill pathogens, and some help to trigger immune responses such as the production of antimicrobial peptides or antibodies. But if you ingested mirror bacteria, many of these defenses would likely fail.
Your gut’s microbiome probably wouldn’t be able to spot mirror bacteria’s reversed molecules, so it won’t trigger the production of antibacterial compounds. Even if they were produced, these substances almost certainly wouldn’t be able to bind to mirror molecules, just as a left glove doesn’t fit on a right hand. Perhaps worst, the failure of these early defenses means it’s unlikely your body would trigger the downstream immune responses required to successfully fight off an infection.
Our immune systems have evolved complex and layered immune responses to bacteria, recognizing the molecular signatures (called pathogen-associated molecular patterns) that are common to many of them and triggering immune responses to limit their invasion. Our bodies would be unlikely to spot invaders with reversed molecular structures. Even if they did, they wouldn’t be able to attack the microbes with their full arsenal of immune defenses, many of which also rely on chiral interactions.
For example, one critical early part of the immune response is the activity of cells such as neutrophils and macrophages, which “eat” bacterial threats and digest them by attacking chiral bacterial molecules with a chiral enzyme. Their digestive enzymes wouldn’t be able to break the chemical bonds of mirror cells, because they have evolved to grab and break those cells’ opposites. It’s likely that macrophages and other immune cells would be less effective at killing mirror bacteria.
That’s only one problem. Your immune system also has an adaptive system of specialized immune cells and antibodies that attack and destroy invading microbes. This system remembers what those intruders look like so it can mount a stronger response if the threat returns.
Such adaptive immune memories rely on chiral molecules. We can’t directly study what a mirror-bacterial infection would look like, but the diseases of people born with genetic defects in parts of the immune system provide clues. One such group of patients has a dysfunctional form of a receptor called MHC-II. Normally this receptor captures fragments of pathogens and signposts them for T cells, but the receptor doesn’t work properly in these patients. Similarly, mirror proteins could not be broken down into those fragments, so MHC-II would not be able to signpost them. Mirror infections therefore might resemble the infection of an MHC-II-deficient patient.
The comparison is not reassuring. These people often die in childhood, overwhelmed by infections caused by the common bacteria and viruses all around us. And this is a case study of failure in just one part of the immune system. Mirror bacteria would probably evade several parts at the same time.
The concern is that, freed from the pressures of immune constraints and the competition of the natural microbiome on our skin and in our gut, mirror bacteria could replicate faster than they are cleared and then, riding the bloodstream, deposit bacterial cells throughout the body. The inside of the human body has enough achiral nutrients for mirror bacteria to grow. A mirror bacterium engineered to use a natural-chirality diet would fare even better. The body would then become a petri dish, like a cadaver—unprotected by living immune cells. What this strange infection would look like precisely is unclear, but the expected result is sepsislike inflammation and death.
As the danger of mirror cells became more apparent, a team of scientists began working on what to do.
Astonishingly, it gets worse. The natural world is full of bacteria—a million cells in a gram of seawater, a billion in a gram of soil. They don’t overwhelm the planet, because they have predators that rely heavily on chiral processes. Viruses called bacteriophages enter bacteria by latching onto surface proteins that they match the configuration of like a key fitting into a lock. The phages kill bacteria, limiting their threat. But if there is no match between a phage and a surface protein, the phage can’t get in. Even if one did get inside a mirror bacterium, none of its replication machinery or genetic material would work there. The bacteriophage would be stuck, alone and isolated, incapable of replicating inside the cell.
Amoebas and other microbial predators, meanwhile, track and swallow bacteria and digest them whole. They’d face the same problems as macrophages in the human immune system: they would be less able to detect mirrored molecules, and even if they managed to swallow one, they’d probably struggle to digest it and use the mirror component parts as nutrients. Even at larger scales—those of plants and other animals—immunity consistently relies on chiral interactions. As a result, many animal and plant species might be unable to fend off mirror bacteria.
There could also be enormous environmental consequences. Cyanobacteria are simple organisms that derive nutrition directly from sunlight and carbon dioxide, and they often don’t require any chiral nutrients. The same would be true for mirrored versions if any were built. But because they would probably be resistant to viruses, there would be much less downward pressure on their populations. As they grew in number, they would compete with other bacteria for scarce ocean nutrients such as iron or phosphorus, significantly reducing the population of natural-chirality bacteria, which would leave species such as marine krill with much less to feed on. If krill populations collapsed, that could in turn drive many larger species such as whales to extinction.
How do we stop this? As the steps toward danger became more apparent in the past several years, a team of more than 150 scientists in different disciplines assembled from around the world and began working to figure out what to do. We gathered in Paris last June to make a plan.
The agreement among researchers in Paris was widespread: mirror organisms should never be created. Laws will be needed to ensure they aren’t, and we must draw red lines around the most dangerous technologies that could enable their synthesis. In the meantime, research funders can help by confirming they won’t support work aimed at building mirror cells—much as they have already committed to not funding research into human cloning.
I started out confused and dubious about this threat, and then I became very concerned. But today I find myself invigorated about our ability to ward off catastrophe—because we’ve spotted this threat so early.
Yes, scientists have made small chiral molecules. But making a complete, functional mirror cell would take extraordinary effort: synthesizing longer and longer biomolecules, making a bacterial chassis from scratch, and creating all the component parts of cellular life, such as ribosomes. Then everything would have to be assembled into a living, working cell. Despite decades of work since the early 1990s, nobody has built an entire standard cell from scratch. We estimate it would require the kind of effort and resources of scientific megaprojects such as the Human Genome Project—which has cost billions of dollars—to make a completely new entity such as a mirror microbe. Building mirror bacteria is a bit like building a skyscraper twice the height of today’s tallest structures: we know technically what needs to be done, but it would be an extremely complex feat of engineering. This fact gives us a golden opportunity to tackle the risk long before it materializes.
Acting now is our leverage. There aren’t many examples of scientists identifying issues with the development of technology before issues emerge. Chlorofluorocarbons were retired from use only after they’d torn a hole in the ozone layer. Thalidomide stopped being prescribed for pregnant women only after thousands of infants were born with birth defects. But we have identified this problem.
In addition to a moratorium on mirror-cell work, we can develop strong modes of governance with international entities that identify and control the chemical constituents of mirror molecules and cells. These agencies could spot whether a lab or a country was accumulating unusual amounts of these compounds, just as they sound the alarm today if a country is stockpiling the components of chemical or nuclear weapons.
Yet we don’t want to limit science in this area completely. Some research in synthetic biology could help with the design and manufacture of novel drugs that could benefit the world. For instance, it may be a good idea to allow scientists to work with certain small mirror molecules but ban the stockpiling of mirror compounds that exceed a certain length. The longer ones can be more easily used to assemble an entire mirror cell.
We won’t figure out where to draw the line or how to solve all these challenges in one go. We can’t make any final decisions on an issue of this importance at any single conference. Much more work is needed to understand the best governance methods that will ensure that the risks can be avoided. But I’m tremendously encouraged by how quickly a large group of scientists and biosecurity experts—more than 300 people attended the Paris meeting either in person or virtually—recognized there was a huge problem and agreed on the urgency of finding a solution.
The risks of this technology are great, but it’s easy to see the people who are working hard to eliminate them. All we have to do is look in the mirror.Author: Josh Fischman. Vaughn S. Cooper. Source
