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They Do It With Mirrors

Recently, 38 scientists called for a ban on research that could result in a killer microbe and an unstoppable pandemic

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Carl Zimmer
Published 13.01.25, 07:27 AM

The consequences could be globally disastrous, according to Jack W. Szostak, a Nobel Prize-winning chemist at the University of Chicago, US, who helped write a 299-page technical report on the risks of the research.

In an accompanying commentary in the journal Science, Szostak and his colleagues warned that an organism created with the new technology could cause “extraordinarily damaging consequences for the environment, agriculture and human well-being.”

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To make such a microbe, scientists would have to build a cell that defied one of the fundamental properties of life on Earth. The molecules that serve as the building blocks of DNA and proteins typically exist in one of two mirror-image forms. But living cells rely on just one form.

Our DNA, for example, has a backbone made partly of sugar. While sugar molecules can exist in both left and right-handed forms, DNA only uses the right-handed molecules.

That’s the reason DNA’s double helix has a right-handed twist. Our proteins, by contrast, are made of left-handed amino acids. This combination is found not just in humans but in every species on Earth.

Scientists are still debating how evolution landed on this arrangement.
In theory, a mirror cell — with left-handed DNA and right-handed proteins — could carry out all the biochemical reactions required to stay alive.

But as far as biologists can tell, mirror cells do not exist in nature or anywhere else. At least not yet.

In recent decades, chemists have discovered how to make mirror proteins. Researchers have been able to weld together right-handed amino acids to create mirror versions of the natural proteins made by our own bodies.

Chemists are now trying to exploit mirror proteins, hoping they can be used to create long-acting drugs for diseases ranging from HIV to Alzheimer’s.

In recent years, scientists have taken even bigger strides in mirror biology. Ordinary cells make proteins by reading a gene, making a copy of the gene’s sequence in an RNA molecule and shipping that RNA to a protein-making factory.

In 2022, Yuan Xu and Ting Zhu, two researchers at Westlake University in China, created mirror enzymes that can produce mirror RNA molecules by reading mirror genes. Similar advances have raised the prospect that scientists could eventually make all the parts required to build a mirror cell, perhaps in 10 to 30 years.

“The creation of mirror-image life is one of the ultimate applications of synthetic mirror-image proteins,” Richard Payne, a chemist at the University of Sydney in Australia, and his colleagues wrote last year.

Several teams of scientists started taking further steps toward mirror cells. “It’s inherently incredibly cool,” said Kate Adamala, a synthetic biologist at the University of Minnesota, US. “If we made a mirror cell, we would have made a second tree of life.”

Aside from being cool, a mirror cell might also be medically valuable. Scientists could programme it to make bigger, more powerful mirror proteins.

Kevin Esvelt, a biologist at the Massachusetts Institute of Technology, US, who studies the risks of biotechnology, had vaguely wondered in the past if mirror cells might pose a risk. As its synthesis became possible, he began to take that risk seriously.

He raised his concerns with biosecurity experts at Open Philanthropy, which funds research on potential threats to humanity such as pandemics and artificial intelligence.

They brought together Adamala and other researchers working on mirror cells, along with immunologists, plant biologists and evolutionary biologists, to talk about the
possible risks.


The discussion felt at first like science fiction to Jonathan Jones, a plant biologist at the Sainsbury Laboratory in Norwich, England. “It took me a while to take it seriously,” he said.

But he eventually recognised the potential for a planetwide catastrophe if a mirror cell escaped containment — either accidentally released from a laboratory or set free as a biological weapon.

The researchers then spent weeks plowing through the scientific literature to see if they could falsify their hypothesis.

“We’ve all done our best to shoot it down,” said Vaughn Cooper, an evolutionary biologist at the University of Pittsburgh, US. “And we failed.”

The trouble with mirror cells is that they could probably evade most of the barriers that keep ordinary organisms in check. To fight off pathogens, for example, our bodies must first detect them with molecular sensors.

Those sensors can only latch on to left-handed proteins or right-handed DNA and RNA. A mirror cell that infected lab workers might spread through their bodies without triggering any resistance from their immune systems.

A victim of mirror cells would harbour a vast supply of the microbes, which could spread to other people and start a pandemic. And it would be one that medicine would be unlikely to stop.

An antibiotic typically works against ordinary microbes by locking on to their proteins or DNA. Such a drug would probably be useless against a mirror cell, because the drug could not get a proper grip on an essential molecule.

All animals rely on similar pathogen sensors to switch on their immune systems, and they would all likely fail to recognise mirror cells.

Plants have their own pathogen detectors, which would also fail. “Essentially, all plants in the world would be unable to detect these bacteria,” Jones warned.

Even if a mirror cell only escaped into a river or the soil, it could wreak ecological havoc. Viruses would be unable to infect it. Amoebae and other predators would find it indigestible.

Unchecked, mirror cells could come to dominate entire ecosystems. “The impact on the food chain would be devastating,” said Deepa Agashe, an evolutionary biologist at the National Center for Biological Sciences at Bengaluru in India.

What makes a mirror cell even more dangerous is that it will be mutating as it replicates, giving it the potential to evolve into an even graver threat.

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