Mirror Bacteria

A Reassessment of Biological Existential Risk

The following is an excerpt from Lesson 7, titled Biological Risk, which forms part of our Making a Difference course.

The previous unit was written in late 2023. This unit revisits and critically examines some of the conclusions drawn earlier, particularly regarding the existential risks posed by biological threats, given newly revealed information since its writing.

The authors of the report argue that the creation of "mirror bacteria" may kill most animals and plants on Earth, including humans. To understand how mirror bacteria might do that, we first need to understand what these bacteria are.

What Are Mirror Bacteria?

Mirror bacteria are bacteria that act and behave the same as normal bacteria, but their molecular building blocks are actual mirror images of normal bacteria.

Mirror bacteria do not currently exist. However, creating them synthetically in a lab has been a goal for a niche group of scientists for years. But now the authors of the report decided to sound the alarm, before that research is successful and the risks of mirror life are irreversibly created.

Our hands have a trait called chirality (or "handedness", in less technical terms). This means that they are three-dimensional objects that are not symmetrical - they look different in a mirror (and from each other). You can place them on each other palm to palm and they seem to match, but if you placed them on top of each other facing the same direction (e.g. both palms facing downwards), they don't match. They're mirror images of each other. No matter how you turn or twist your hands, you can't make them identical - it's an inherent structural property of your hands.

Hands - Chiral

This is different than, say, your whole body. If you look at a mirror (and are not wearing a watch or any other asymmetric accessories) - your mirror image doesn't look that different from you. if you turned your mirror image around, it would roughly look just like you (if we ignore small asymmetries).

Body - Achiral

To describe this difference, we say that each of your hands is chiral (it looks like the opposite of its mirror image), yet your whole body is achiral (it looks like its mirror image).

It turns out that at the molecular level, most of the building blocks of life are chiral. Your DNA (the molecules that store your genetic information), RNA (the molecules that help express that information in the real world), and proteins (the overwhelming majority of all functioning machinery in your body) all look different from their mirror images, even if they build larger structures that appear roughly symmetrical (like you).

DNA - Chiral

RNA - Chiral

Proteins - Chiral

Interestingly, all building blocks across all life on Earth appear in only one direction. Bacteria, plants, animals like yourself, and the viruses all around us - we're all made of components with the same chirality. In our hands analogy, it's as if all life were built out of right hands - and left hands were nowhere to be found across the world. Why this is the case, and whether this is inevitable or a coincidence - are highly debated questions in biology. But there's no question about the empirical fact that the DNA, RNA, and proteins in every living organism we've ever seen have the same chirality, or the same "handedness".

Now that we understand all that, we can understand mirror bacteria. Mirror bacteria are bacteria - single-celled organisms that are responsible for about half of all human disease - whose molecular components would be the mirror image of those found in nature. As an organism, it would behave identically to regular bacteria, but its building blocks would all be reversed.

Why Are Mirror Bacteria Dangerous?

In the macroscopic (large-scale) world

we're used to, chirality doesn't matter.

If someone punches you, you don't

care about the chirality of their fists'

molecules - it's the sheer mass

colliding with your body that matters.

But in the microscopic world bacteria

live in, chirality is everything. The

molecular machinery that allows organisms to eat each other, attack each other, and more - is usually sensitive to chirality. If it were to come across a mirror image of a target it's used to, it just wouldn't interact.

A mirrored version of a ubiquitous bacteria like E. Coli would proliferate widely across the world and inside all animals, while avoiding predation and immune systems that keep other bacteria at bay. As our immune systems fail to respond appropriately, the infection would prove fatal to most complex life.

A neutrophil failing to detect a mirror bacterium

Imagine that someone was to create a mirror image of E. Coli - a ubiquitous bacteria that is all around us (in its non-mirrored form). This mirror E. Coli would proliferate widely - much like normal-chirality E. Coli, which is found almost anywhere in the world, on every surface and inside every animal. But as opposed to normal E. Coli, because it is mirrored, it would be immune to predation, animal and plant immune systems, and pretty much anything keeping existing bacteria at bay. The scientists argue that it would continue to replicate and proliferate far more than any other bacteria - consuming critical resources, clogging our arteries, and wreaking all kinds of havoc that an unstoppable self-replicating machine might cause. Our bodies would be incapable of staving off the infection - since most of our defenses are blind to it, leaving us like children with untreated "bubble boy" disease. As opposed to most diseases, that only affect a small number of animal or plant species, mirror bacteria could infect and kill most complex life.

Many people hear of this and suspect that something doesn't make sense. If microscopic interactions depend on chirality - won't the mirror bacteria need mirrored nutrients (that don't exist in nature) to survive? And therefore won't it be unable to survive outside of a lab setting, making it inherently safe? Indeed most of the nutrients that many bacteria like E. Coli consume, are chiral - and a mirrored version wouldn't be able to consume them naturally. But sadly, we have experiments showing that E. Coli (and other bacteria) can survive only on achiral nutrients that are common in both multicellular hosts and in many external environments - and therefore, so could mirrored E. Coli. Furthermore, we have other experiments showing that when needed, E. Coli can evolve to consume nutrients of opposite chirality - so after it starts proliferating in its natural form, it may soon start to consume all of our nutrients as well. And finally, even if all of these were not true - scientists already know how to modify bacteria intentionally to be able to consume opposite-chirality nutrients, so once a natural mirror bacteria exists, it'll be easy for malicious actors to make it even easier for it to thrive in the wild.

How Easy Is It to Create or Protect Against?

The good news is, it is not possible to create mirror bacteria just yet. The bad news is that we're not totally sure how long it'll be until it is.

The authors of the report estimate mirror bacteria could be created within 15 to 30 years - but admit it could be earlier or later; they're not really sure. Countermeasures to protect us from mirror bacteria can be created, but they would likely only help protect a small portion of humanity, and are extremely unlikely to successfully protect our crops, wildlands, and ecosystem.

The group of scientists sounding the alarm estimated that at the current level of investment, mirror bacteria is about 15 to 30 years of research away. If well-intentioned scientists stopped research towards creating mirror bacteria (as the report authors pledged to do), that timeline could be stretched further. However, that timeline could also be accelerated by, for example, rogue nations recklessly rushing ahead with this research in an effort to gain leverage through the ultimate threat: potentially triggering a catastrophe far more devastating than any nuclear weapon. So while mirror bacteria is still very difficult to create, leaving room for a lot of impactful action today, research towards how to create mirror bacteria could be irreversibly discovered and proliferated - and once we know how to do so, it is expected not to be very difficult to replicate.

Timeline of Potential Creation of Mirror Bacteria

But could we prepare countermeasures against such bacteria to mitigate the harm? Yes, but it currently seems that the benefits would be fairly limited.

Existing countermeasures like antibiotics won't work because they, too, are sensitive to chirality. But we could develop new ones - like mirrored antibiotics or mirror phages (viruses that attack and kill bacteria). These countermeasures could also be developed without advancing the science on creating mirror bacteria, which is important. As a result, they're a promising and worthwhile course of action to take. However, we shouldn't overstate the capability of such countermeasures. If a disease only affects humans, one could imagine delivering a medication to all humans around the world to prevent most of the harms (though, of course, we failed to do that comprehensively in response to COVID). If a disease threatens to eradicate all complex life - there's no foreseeable practical way to provide medicine to all animal and plant life across the globe. Countermeasures may be helpful in protecting a small fraction of the world's ecosystem, and that fraction would need to discover a way to survive longer-term without nature and large-scale agriculture. So while countermeasures can help, even in the best case - they're not remotely as valuable as preventing the creation of mirror life to begin with.

But Why Did They Announce It Publicly?

The decision to announce this threat was controversial. Many national security experts we've spoken to are convinced that North Korea (and possibly other countries) will now race to create mirror bacteria and that the announcement was a mistake.

The authors of the report claim that while this announcement involves risks, the alternative would be worse. Prior to the announcement, there was already a mature, international, ongoing effort to create mirror bacteria. As noted, this effort was expected to successfully create mirror life in 15 to 30 years. If no one had alerted scientists in this domain to the risk, they would have obliviously walked straight into creating something that could kill everyone. If someone had noticed the risks later on but prior to the creation of mirror life, we'd be in the same situation we are now, but with fewer technical hurdles preventing bad actors from being able to create mirror bacteria themselves. If the scientists had just tried to alert everyone who needs to know but not the public, the set of scientists doing relevant work is large and international enough that it would undoubtedly leak, but it would seem more shady and unreliable than being forthright with the public about it.

So while "the right decision" is hard to reach consensus on, those were the primary considerations.

How Sure Are We of the Risk?

This initial publication makes a strong case for mirror bacteria being a risk of unprecedented scale. Many of us (including the course staff!) don't have the technical expertise to evaluate the claims directly, so we need to rely on experts, just like we discussed in lesson 6. The author list includes world renowned experts in virology, immunology, biochemistry, and other fields relevant to evaluating the claims. It includes multiple Nobel laureates in relevant domains. Perhaps more importantly, the original announcement includes most scientists working on mirror life globally - and it was supported by a virtual consensus among an even broader group of scientists and biosecurity professionals several months later. There hasn't been such an agreement on risks in the history of biological research.

However, it is still early days. At the time of writing (early 2025), the original announcement and supporting evidence has only recently come out - and scientific discussions take time to settle. So it's still possible that some subtle assumption turns out not to be true - but for now, we should at least be taking this risk very seriously.

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