Scientist Kate Adamala doesn’t remember exactly when she realized her lab at the University of Minnesota was working on something potentially dangerous — so dangerous in fact that some researchers think it could pose an existential risk to all life forms on Earth.

She was one of four researchers awarded a $4 million US National Science Foundation grant in 2019 to investigate whether it’s possible to produce a mirror cell, in which the structure of all of its component biomolecules is the reverse of what’s found in normal cells.

The work was important, they thought, because such reversed cells, which have never existed in nature, could shed light on the origins of life and make it easier to create molecules with therapeutic value, potentially tackling significant medical challenges such as infectious disease and superbugs. But doubt crept in.

“It was never one light bulb moment. It was kind of a slow boiling over a few months,” Adamala, a synthetic biologist, said. People started asking questions, she added, “and we thought we can answer them, and then we realized we cannot.”

The questions hinged on what would happen if scientists succeeded in making a “mirror organism” such as a bacterium from molecules that are the mirror images of their natural forms. Could it inadvertently spread unchecked in the body or an environment, posing grave risks to human health and dire consequences for the planet? Or would it merely fizzle out and harmlessly disappear without a trace?

In nature, the structure of many major biomolecules is right- or left-handed, although it’s not clear why life evolved this way. It’s a property known as chirality that was first discovered by French scientist Louis Pasteur in 1848. For example, DNA and RNA are made from “right-handed” nucleotides, and proteins are made from “left-handed” amino acids. Just as a right-handed glove cannot fit a left hand or how a key precisely fits a lock, interactions between molecules often depend on chirality, and living systems need consistent patterns of chirality to function properly.

In a mirror cell, all its molecules would be replaced with mirror-image versions. Such a development is hypothetical; even creating a synthetic cell with natural chirality that mimics its normal living counterparts isn’t yet possible, but it’s an active and exciting area of research that Adamala and several other research groups are pursuing