Scientists abandon dream of creating ‘mirror life,’ which could turn into a nightmare

In his 1970 novel Spock Must Die!, based on the Star Trek universe, James Blish recounted how a glitch in the Enterprise’s teleporter created a duplicate of the famed Vulcan scientist, indistinguishable from the original to the naked eye but with all of its molecules reversed like a mirror image. To survive, the second Spock was forced to synthesize mirror-image amino acids—building blocks of proteins—because he could not metabolize normal ones.

It was no wild fantasy. Many molecules can assume two alternative configurations, called left and right, which are mirror images of each other, like two gloves in a pair. All life on Earth is based on left-handed amino acids, while DNA and RNA carry only right-handed sugars. Ever since the microbiologist Louis Pasteur discovered this property, called chirality, in 1848, science fiction has speculated about it.

But this intriguing field has also given rise to dreams in real science: what if mirror-like beings existed, with their amino acids and sugars oriented backwards? Synthetic biology laboratories have toyed with the possibility of constructing mirror bacteria. Now, however, these same scientists are abandoning the idea because of the possible catastrophic consequences that could turn the dream into a nightmare.

The molecular world upside down

There is no apparent biological reason for terrestrial life to have made this choice. An excess of left-handed amino acids has been found in some meteorites, which could have conditioned biology if those ingredients arrived from space. But everything must remain that way for life to function, since biological molecules fit together like puzzle pieces. Like the false Spock, a mirror animal could only digest mirror food.

Mirror molecules are being synthesized in laboratories that may have interesting properties. “There are researchers who are building mirror proteins and nucleic acids to determine whether they can be used for pharmaceutical purposes,” explains John Glass, head of the Synthetic Biology group and director of the La Jolla campus of the J. Craig Venter Institute in California.

Glass was part of the team that created the first bacterial cell with a synthetic genome in 2010, an achievement that has also been a boost to the possibility of producing mirror bacteria. But in 2024, a working group co-chaired by Glass brought together nearly 40 renowned researchers from 26 institutions in nine countries to ponder one question: should this goal be pursued?

Potentially lethal and invasive

The group’s conclusion, based on a comprehensive 300-page technical report, was published last December in the journal Science: “Our view is that mirror bacteria and other mirror organisms should not be created,” they wrote. The reason for this recommendation is summed up in the impact on two areas: health and the environment. “Our analysis suggests that mirror bacteria would likely evade many immune mechanisms mediated by chiral molecules, potentially causing lethal infections in humans, animals and plants,” the signatories warned, adding: “We cannot rule out a scenario in which a mirror bacterium acts as an invasive species in many ecosystems.”

But if Spock had to synthesize his own special food, how could a mirror bacterium survive on a world that was chirally hostile to it? This was one of the reasons that had until now kept some scientists skeptical about the risks of mirror bacteria, along with the idea that any microbe so created could be contained, if at all, by embedding certain deficiencies in its metabolism that would prevent it from living outside its small laboratory habitat.

However, many bacteria, such as the tiny Escherichia coli that powers biology labs, can live in environments devoid of chiral nutrients, which are abundant in nature, they write. As for biocontainment, “laboratory accidents occur with some regularity, even in high-containment labs, whether due to human error or equipment failure,” they write, noting the possibility that bacteria could evolve to free themselves from their metabolic shackles or that someone could break them loose on purpose.

Continue the discussion

“Our December paper in Science has attracted a lot of attention from both the press and other scientists,” Glass says, adding that almost all reactions have been supportive of the proposal to abandon the creation of mirror bacteria. “It is noteworthy that every single researcher we know who has received funding to build mirror bacteria has signed our paper.”

According to Glass, this is the case of Kate Adamala, a synthetic biologist at the University of Minnesota. Adamala, co-author of the report and the Science article, says that creating mirror life has not been a priority for her, but she is blunt: “Given the potentially extraordinary risks we have identified, I think no one should be working to build mirror bacteria.” She appreciates that the consequences have been considered before it is too late, something that, she regrets, does not always happen.

“We were pleased to see prominent scientists and policymakers take these risks seriously and join our call for further dialogue,” said another author, microbiologist and molecular geneticist Vaughn Cooper of the University of Pittsburgh. The discussion continues at a conference in Asilomar, California, marking the 50th anniversary of an event that examined the dangers of genetic technologies. In June, a meeting at the Pasteur Institute in Paris will include a public seminar to “develop the arguments of the technical report and provide a broader context for mirror life,” Adamala said.

Drawing the red line in the “grey zone”

The biologist is reassuring: “No one is working on building mirror bacteria today.” However, as Ting Zhu, a biochemist at Westlake University in China, one of the most prominent researchers in the manufacture of mirror biomolecules, points out, the synthesis of a complete mirror cell would not be technologically possible “in the future that we can predict.” Zhu, who has not participated in the working group or in the publications of his colleagues, says he also supports the cautious approach.

Zhu’s work involves creating a mirror version of the molecular machinery of DNA and RNA to make mirror proteins. Experts agree that this research does not entail any risk and should continue; the red line is creating something capable of self-replication: “It is at that point that the work becomes potentially very dangerous,” says another of the co-authors, Jonathan Jones, from the Sainsbury Laboratory in the United Kingdom and a specialist in plant defenses against infections.

However, Adamala admits, “there is a grey area between the two, and a broad international discussion is needed on where to draw the line.” The key to the difference lies, according to Glass, in a quote from Harvard synthetic biologist Pamela Silver: “Yogurt can make more yogurt, but shampoo can’t make more shampoo.”

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