Ellen Phiddian
Cosmos science journalist
Late last year, a group of 38 scientists sounded an alarm on a potential technology that could “cause unprecedented and irreversible harm” to the world.
Their concern wasn’t weaponry, or pollution. It was asymmetry.
The technology – called “mirror life” – is now sparking talks in the scientific community, looking at its risks and how to control them.
But what is mirror life – and why does it have researchers so scared?
What is mirror life?
To understand mirror life, it’s best to start with mirror molecules.
Some molecules have a geometric property called chirality. It’s a type of asymmetry, where a shape is not identical to its mirror image.
If an atom in a molecule – say, a carbon atom – is bonded to 4 different components, it’s possible to arrange those components in 2 different ways around the central atom. You could make 2 different molecules from all the same components and bonds.
If you’ve ever played Tetris, you’ll be familiar with chiral shapes: the L-block, for instance, can fit into some pockets that its mirror image block can’t – even though they’re both made from squares connected in the same way.
Hands are also chiral: your right and left hand are both made from the same fingers, connected in the same way, but they’re not identical to each other. Chemists often distinguish between mirror molecules by referring to them as left- and right- handed.
Chirality can pop up in all sorts of molecules, but it’s most pertinent in those that contain carbon, because of the way that carbon atoms tend to bond. Biological molecules, like proteins and DNA, are made from chiral molecules. In fact, they’re all “homochiral”: they all share the same asymmetry. DNA, for instance, is right-handed, while proteins are made of almost entirely left-handed molecules.
We don’t know why all living things are homochiral. There’s no chemical or biological reason an organism made from mirror molecules – say, a mirror bacterium – couldn’t exist, grow, and proliferate in the world.
In fact, given some time and a lot of resources, it would be possible for scientists to make synthetic “mirror life”: bacteria made from left-handed DNA and right-handed proteins.
This is what is concerning the scientific community. Last December, 38 researchers co-authored a paper in Science, calling for a halt to mirror life work.
Why is mirror life concerning?
Mirror bacteria would be able to grow and proliferate just like regular bacteria. But unlike regular bacteria, we haven’t evolved any defences against them.
Most of the ways our immune system fights bacteria involve homochiral molecules, according to Professor Michael Kay, a biochemist at the University of Utah, USA, and one of the paper’s co-authors. The immune system has evolved to be highly specific, meaning it’s very sensitive to chirality.
“Since almost all of the immune system has this chiral requirement, you would have something that could escape many different aspects of immunity all at one time,” Kay tells Cosmos.
“A bacteria that develops antibiotic resistance to one antibiotic – that’s one step. This would simultaneously be avoiding all these different arms of the immune system. So that is an unprecedented potential.”
Generally, pathogens that can manage one form of immune escape are extremely dangerous, but mirror bacteria would be able to escape multiple different parts of the immune system.
“There are some aspects of immunity in occasional, specialised cases that seem to be able to operate independent of chirality, but it’s a very small portion of the overall immune response,” says Kay.
Humans would not be the only things threatened by mirror life. All living organisms would be vulnerable.
“You could imagine a series of countermeasures and responses to try to protect humans against something like this, although that would be incredibly challenging,” says Kay.
“But it’s unimaginable how you would protect the ocean, or crops, or other ecosystems.”
This is why Kay and his collaborators are arguing that mirror life shouldn’t be created in the first place. They don’t think labs could be made secure enough to control the risk of mirror bacteria escaping.
“It just makes so much more sense, with that type of threat, to simply prevent it – rather than to try to respond to it once the genie is out of the bottle,” says Kay.
Is mirror life an imminent threat?
No. While researchers have been making mirror proteins, a whole mirror bacterium would take at least 10 years more work and very dedicated resources, according to the researchers.
“Technologies are starting to be developed where this really seems like it could be feasible in our lifetimes, but it’s not imminent, and the resources required to do this are going to be immense,” says Kay.
“This is not something that somebody could work on in their garage, away from a regulatory infrastructure. It’s going to require very organised, heavily resourced institutions like the NIH or the Wellcome Trust.”
This broaches another question: if it’s so difficult to do, and so potentially dangerous, why would any institution try it?
“There’s a growing interest and growing promise in mirror image therapeutics – mirror peptides, proteins, nucleic acids,” says Kay.
Because of their immune resistance, these proteins and other biological molecules are promising medicines. They don’t pose any of the risks that a whole mirror cell would.
“These are inert, not capable of replicating or evolving. They’re not alive,” says Kay.
Non-mirror bacteria are often the easiest way to manufacture medicines – mRNA vaccines, for instance, are made with bacteria.
“The promise of a mirror cell is that it has the potential to be a factory for these types of therapeutics,” says Kay.
But it’s possible to make the mirror therapeutics without mirror bacteria. That’s how they’re currently being made. In fact, that’s how Kay, who researches mirror therapeutics, is currently making them.
“It is important to note that currently, all of these things are made by chemical synthesis techniques, and that technology is rapidly evolving,” says Kay.
“In a bit of an irony for this whole situation with mirror life, those technologies are going to have to get a lot better in order to get to the level of efficiency necessary to make something as gargantuan and incredibly complicated as an entire cell.
“If that technology were to develop such that you could actually make a cell, that means the technology is good enough that you probably don’t really need the cell anymore.”
So beyond scientific curiosity, Kay doesn’t think there’s likely to be any pharmaceutical advantage to making mirror life.
How do we prevent the hazards of mirror life?
The researchers behind the Science paper are calling for open discussions on mirror life.
“We really want to hear from everybody who has an insight or data, and make sure that we have the most robust evaluation of potential risks possible,” says Kay.
The group believes it’s possible to regulate research so that mirror life can’t be made, but the promising work on mirror molecules can continue.
“That’s really going to be a big focus of these upcoming conversations and conferences with a broader group of stakeholders – including regulatory agencies, governments, funding agencies, as well as other scientists and other members of the public,” says Kay.
There are precedents for preventing research like this. Kay cites restrictions on nucleic acids, which can be used to make dangerous viruses, as an example. Organisations like the International Gene Synthesis Consortium have made protocols for screening and vetting people who sell and buy these materials.
“That’s a very minor step that has not impeded any legitimate research, but creates a little additional barrier against anybody who might want to do something with bad ends in mind,” he says.
The group doesn’t have a clear proposal for what good mirror life regulation would look like – that’s what they’re hoping will come out of these discussions and research. The amount of time and resources needed to make a mirror cell is an advantage here: the world has time to put the right rules in place.
“If we can get a good agreement among all those big players in funding and supervising research, it’s extremely difficult to imagine how a bad actor could sneak around that,” says Kay.
