Have you ever heard of mirror bacteria? Mirror bacteria are synthetic organisms in which the molecular structure found in nature is reversed. It is not currently possible to create mirror bacteria. Nonetheless, dozens of scientists are warning of the dangers of mirror bacteria research, noting that, with no natural enemies and access to essential achiral nutrients, mirror bacteria could escape and establish themselves in the wild. Such an event could mirror the scale of unprecedented environmental disasters or biological warfare, as they would be immune to natural countermeasures and potentially engineered to survive adverse conditions.

For context, synthetic biologists have made significant breakthroughs in synthetic (artificial) biology, such as encoding data in DNA and designing minimal genomes. Many researchers believe the field promises advancements in medicine, material science, and a better understanding of life. The concept of mirror life demonstrates that mirror bacteria are hypothetical organisms with reversed molecular chirality. Chirality essentially means ‘mirror-image, non-superimposable molecules’, and to say that a molecule is chiral is to say that its mirror image (it must have one) is not the same as itself. Whether a molecule is chiral or achiral depends upon a particular set of overlapping conditions.

Is that glimpse at mirror bacteria confusing enough for you? These ideas are undoubtedly heavy on the brain and not all that easy to make sense of. It appears it is either really complicated or frighteningly simple. Either way, mirror bacteria are immune to natural countermeasures and potentially engineered to survive adverse conditions. That certainly sounds like biological warfare, capable of putting humans, plants, and animals at risk of exposure to dangerous pathogens. Is that what promoted a group of 38 scientists working in nine countries to publish a report in Science sounding the alarm about the potential creation of mirror bacteria?

Though the science and technology needed to create mirror bacteria is a decade or more away, advances in synthetic biology have been astounding. In the last fifteen years, synthetic biologists have stored books, images, and even videos in DNA. They have developed the ability to modify and engineer genes with incredible accuracy and even created an organism with chromosomes designed using a computer and synthesized in the lab. The researchers note these advances, where researchers are free to follow their whims, have allowed them to develop effective drugs against diseases like malaria, innovate lightweight, biodegradable, and high-strength materials such as artificial spider silk, and bolster their understanding of how life forms. Importantly, researchers John Glass, PhD, and Kate Adamala, PhD—two of the 38 authors warning about the dangers of mirror bacteria—reported that these breakthroughs were unexpected in many cases and would not have happened if scientists could not conduct their research freely. Having said that, they added:

“However, we recently joined a number of other scientists in calling for a certain line of research to not be pursued: work that could result in the creation of “mirror bacteria.” These are bacteria made of all components that natural cells possess, but with every biopolymer being of opposite stereochemistry. We are passionate defenders of allowing scientists to conduct their research with as few limits on intellectual curiosity as possible, and calling for a ban is not something that we do often or lightly. However, every rule has exceptions, and this is one of them. Unless compelling evidence emerges showing that mirror bacteria do not pose unacceptable risks, we believe research to develop mirror life should not continue.”

Glass and Adamala describe the allure of mirror life as rooted in its potential to advance scientific understanding and innovation. They note that the complexity and mystery of life have long captivated scientists, driving efforts to reconstruct it from scratch to deepen our knowledge and expand its applications. Synthetic biology, particularly through the creation of synthetic cells, provides a pathway to achieve this. These artificial cells, designed using synthesized or assembled natural molecules, serve as adaptable tools for innovation—ranging from self-healing concrete to minimal cells exploring life’s foundational principles.

They explain that minimal cells, stripped of non-essential genes, offer a simplified platform to study cell biology and test drug effects without the interference of natural cellular complexities. Their inability to survive outside the lab ensures a controlled environment for research, making them indispensable in synthetic biology. Motivated by these possibilities, the “Build-a-Cell” community was launched in 2018 to unite researchers in the pursuit of synthetic life. Seems safe enough, right?

Not surprisingly, mirror cells—again, synthetic cells built with reversed chirality—represent a frontier in this build-a-cell field. After all, chirality, or the left- or right-handedness of molecules, is a fundamental aspect of biology. While nature favors specific orientations (e.g., left-handed amino acids and right-handed sugars), mirror molecules are their structural opposites synthesized in labs. Mirror cells, composed entirely of such molecules, would be biologically sequestered and unable to interact with natural systems. Glass and Adamala note that this isolation offers unique advantages: reduced contamination in research and the creation of mirror drugs that resist natural metabolic breakdown.

If research continues unrestrained, the eventual development of mirror bacteria constructed from these mirror cells promises engineering feats of unparalleled complexity. Initially, this prospect thrilled researchers, but the realization of its potential dangers tempered their enthusiasm. Mirror bacteria, immune to natural predators and human immune responses, could pose catastrophic risks if released into the environment. Despite the allure of understanding life from a new perspective, these risks challenge the continuation of this ambitious research.

In a nutshell, unchecked mirror bacteria dings like something out of a science fiction movie. Mirror bacteria are uniquely dangerous because they would not be subject to the natural controls that regulate bacterial populations. Critical factors like competition with other bacteria and predation by bacteriophages (viruses that infect bacteria) would not affect mirror bacteria because of their molecular incompatibility. This lack of natural checks could result in uncontrolled, exponential growth, leading to invasive populations that disrupt ecosystems, agriculture, and biodiversity. Ok, that sounds potentially catastrophic—like AI invading nature—but that’s not all.

Additionally, the immune systems of plants and animals would be unable to recognize or combat mirror bacteria, as their molecular structures would render them “invisible” to immune defenses. This vulnerability parallels severe immunodeficiency in humans, leaving organisms highly susceptible to microbial infections with potentially catastrophic consequences. Another critical danger lies in unpredictability. Once created, mirror bacteria could replicate and evolve in unforeseen ways if released into the environment, amplifying their risks and creating challenges that science cannot begin to anticipate or mitigate. Describing what steps she recommends to prevent the catastrophe that would ensue from the development of mirror bacteria, Yale School of Medicine’s Isabella Backman wrote:

“One can take all kinds of measures to reduce risks, but again, it’s fundamentally impossible to avoid all of the consequences once bacteria are able to replicate and mutate. No mirror bacterium could be made provably safe—accidents happen at research laboratories and pathogens escape and can cause problems of different scales. As I’ve heard one of my fellow authors put it, the only safe mirror bacterium is one that doesn’t exist.”