“Mirror life” poses extreme existential risk to the world, scientists warn

Just when you thought you had enough to worry about, scientists came up with a new world-ending anxiety for us all. A dire warning about something nobody outside the relevant fields knew anything about. A risk easily confused with the TV series “Black Mirror,” or the virtual reality world “Second Life.”

Last month, a report in Science authored by 38 scientists representing various fields, and accompanied by a 288-page technical report again put together by multiple authors, called for the “the global research community, policy-makers, research funders, industry, civil society, and the public” to hold broad discussions on the dangers that could be posed by bioengineering hypothetical organisms, called “mirror life.”

Though it may sound like something cute from “Alice in Wonderland,” mirror life refers to synthetic organisms modeled after bacteria — but created with building blocks that are mirror images of the constituents of DNA, RNA and proteins as they exist in nature. The building blocks of life follow certain rules and mirror life is basically the inversion of it. And it seems theoretically possible to do it, but experts are now warning it could be opening Pandora’s box.

“It’s starting to seem like the enabling technologies [for mirror bacteria] are in the process of being developed, and that inevitably, this would be done unless we make a conscious decision to regulate it,” Dr. Michael Kay, an expert on mirror pharmaceuticals, and a professor of biochemistry in the Spencer Fox Eccles School of Medicine at the University of Utah, told Salon in a video interview.

The people behind the Science policy forum report and the technical report make up an illustrious group including two Nobel laureates and other names not typically associated with risk aversion or the precautionary principle, such as that of Craig Venter, the thrill-seeking founder of the Human Genome project. Venter replicated the DNA of a bacterium in 2008 and in 2010 announced the creation of a self-replicating synthetic genome, or DNA, in a bacterium taken from a different species, spurring a bioethics investigation of the developing field of synthetic biology by then-President Obama that identified limited risks.

With mirror bacteria specifically, the risks, while still hypothetical, are not limited at all.

Proteins are left-handed and DNA is right-handed

The functions that different components of life, such as proteins or DNA, are able to achieve is very much based on their structure. One aspect of that is the orientation of their parts. As it happens, many aspects of life exhibit chirality, or “handedness.” Your hands are chiral body parts, because when placed over one another, they line up perfectly yet are shaped reflectively.

Amino acids, which make up proteins, or nucleotides, which make up DNA and RNA, are the same way. Chirality in molecules means they have a specific orientation in space such that the mirror image of the molecule in question cannot be perfectly superimposed on the original. Effectively, and functionally, a molecule and its chiral mirror image are two different molecules.

In the real world we live in, for reasons we don’t understand (perhaps for no reason at all), the individual letters that make up the code of DNA and RNA all follow a right-handed orientation, while the amino acids that make up proteins are all left-handed. So if you were to engineer synthetic mirror image versions of these, the amino acids would have right-handed chirality and the DNA would have left-handed chirality. Synthetic biologists have been eager to take inspiration from existing molecules and use it to create tiny mirror image organisms, or mirror bacteria.

The idea of mirror life was first floated in 1860 by Louis Pasteur, of vaccination, fermentation and pasteurization fame. But the march towards reality began thirty years ago, when chemistry researcher and chemical protein synthesis pioneer Stephen Kent, now retired from the University of Chicago, published a seminal paper describing his synthesis of a mirror version of an HIV protease. A protease is an enzyme that cuts proteins (polypeptides) into smaller parts, called peptide chains. In HIV, this allows the smaller proteins produced to combine with the genetic material of the virus to form copies of itself.  

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“[Kent] really laid the basis that mirror image peptides could be valuable therapeutics, by showing that these are not recognized by proteases in the body,” explained Kay, who was inspired by the chemist’s work.

The mirror protease only works on mirror peptides, which means, by the law of mirror-image symmetry that applies to chiral molecules, that regular proteases would likewise be unable to cut down mirror-image peptides. This might make therapeutic treatments that can last longer in the body, what Kay calls “stealth therapeutics.”

This was the starting point for the idea that we might eventually develop an entirely new class of drugs based on mirror image proteins or other components of life. That is, until some researchers began to consider the risks.

If everything that occurs at the microscopic, molecular level in plants and animals and other life forms occurs as a result of the precise structure that allows molecules like enzymes and hormones to do their jobs, what happens if you create a “backwards” molecule, and then a form of life based on such mirror molecules?

Well, the possibilities are actually pretty horrifying.

A fully mirror organism “could essentially avoid the immune system entirely,” Kay said. Not just the human immune system, but Nature’s immune system, too: “All the various ecological factors that keep bacteria in check, (like viruses known as phage that attack bacteria), antibiotics, competition with other organisms, things that keep any one bacteria from overgrowing … that delicate balance could be upset.”

Back in the 1990s, when a few articles began to float this science fiction-ish, dystopian idea — imagine a bacteria that could wipe out all the plants and the animals that eat them, including humans, and to which none of us have any resistance —  the question was more philosophical or speculative than anything else.

But now, thirty years later, our ability to shape biology has increased incredibly, from gene-editing tools like CRISPR to lab-grown organs. Let’s be clear: like science fiction, mirror bacteria  — full mirror organisms capable of self-replicating and taking on all of our immune systems — don’t exist yet in the real world. But other mirror stuff does. 

Kay has been working on mirror peptides (small proteins) for around twenty years, with his lab now specializing in mirror peptides that could act against viruses, with a mirror peptide HIV drug in clinical trials in humans right now. But mirror bacteria, which would be living organisms capable of self-replicating, not just little bits of protein, are what Kay and his fellow scientists are concerned about.

One of these is immunologist Dr. Timothy Hand, associate professor of pediatrics and of immunology at the University of Pittsburgh.

“The way that the immune system does this is by sensing molecules that are made only by bacteria and viruses (and required for their function) and distinct in structure from anything your body makes. The issue is that many of the bacterial and viral molecules are ‘chiral’ and the mirror versions won’t be seen by the immune system — so they could colonize a human (or animal) in huge numbers before the immune ‘alarm’ is set,” Hand told Salon in an email, highlighting another potential, major problem: It could completely eliminate immune responses from T cells.

“T cells are activated by little pieces of bacterial and viral proteins, called peptides, that get displayed on the surface of infected cells,” Hand explained.  “The key issue is that for this to work, proteins need to be broken down by enzymes called proteases. It seems clear that proteases do poorly in breaking down mirror proteins, so T cell responses would be severely curtailed. T cell responses are also very important, people with substantial deficiencies in T cell function typically require bone marrow transplants to replace their immune systems in order to live normal lives so a failure of T cells to respond to mirror bacteria could be very serious.”

Although he stressed that it’s entirely speculative at this stage, young children, whose microbiome develops gradually from the time they are born to about age three, could theoretically be at even greater risk as the immature microbiome lacks the stable ecosystem of bacteria that in older children and adults resist colonization by new bacteria, including infections.

Is mirror life already here?

While life in 2025 may feel at times like we’ve stumbled through Alice’s looking glass, mirror life is not here yet. At the moment, it’s a hypothetical creation. However, the technical obstacles to realizing mirror life are not insurmountable, and the authors of the Science policy forum report believe that they will be overcome within as little as a decade. That’s why they feel that now is the time to urgently decide how we want to regulate work that might produce such little Frankenstein’s monsters.

“We have a lot of time to be very careful, to bring in all stakeholders, really hear a diversity of opinions, and try to build an international consensus,” Kay said. Surprisingly, given the amount of media attention the report has garnered already, the mirror life working group he’s part of only assembled within the past year; Kay has only been involved during the last six months.

“This can’t be something that the U.S. does alone. It has to be something that’s really done globally and our panel of scientists on this article were already a quite international group,” Kay told Salon. That said, it will be interesting to see what level of engagement the group gets from outside the European, and North American scientific community. “We have this rare opportunity where it’s not imminent, so we have time to be calm and thoughtful and inclusive — but it’s also not science fiction. We’re starting to see the technologies come into place where this could really be a reality in our lifetimes.”

Kay believes it’s best to figure it out calmly before “anybody’s research career or any company” depends on it. The group is working with a public relations organization that more typically represents big tech companies.

The mirror peptides that are the focus of Kay’s work, he said, was not remotely the same as mirror bacteria and he denies the suggestion that the researchers may be trying to get ahead of potential public concern that could conflate mirror peptides, a new and positive category of drugs, with mirror bacteria. Though that certainly is a potential confusion well worth clarifying. So long as the discussion the researchers are calling for results in regulation or prohibition that ensure mirror bacteria are not used for the easier production of mirror peptides, a shortcut Kay says is not necessary, mirror peptides are not dangerous at all.

“There’s a fundamental, very solid line between a chemically produced, relatively simple [mirror] molecule, like a peptide or a protein or nucleic acid [and mirror bacteria]. You make it once and the whole benefit is it’s pretty inert in the body. It just kind of sits around and it ends up in the feces or urine, but basically it doesn’t really interact with the body. It just interacts with the pathogen or the disease. It can’t self-replicate,” Kay told Salon.

In fact, mirror peptides might prove extremely useful, for example by allowing biologics, an increasingly important category of medications, to work much better than they do now.

“Amongst the things that keep me up at night, mirror bacteria are not that high,” Hand said, nevertheless echoing Kay’s sentiment that now, before the technology to produce them exists, is precisely the right time to consider how best to regulate this tricky, “backwards,” hypothetical opponent that could be hard for our immune systems to sense and fight before it’s too late.