Hold out your hands, palms up, and move them so they are on top of each other. With a little experimentation—and perhaps a few rather flamboyant gestures—you’ll find that no matter what you do, your hands will not perfectly align. Congratulations, you’ve just demonstrated chirality.

Chiral objects are non-superimposable mirror images of each other. Chirality is not simply a feature of limbs; it is a trait shared by the molecular building blocks of life—from DNA to sugars to proteins. It dictates how molecules and, in turn, cells, operate and engage with each other and their environments. For example, chirality influences the way immune cells recognize molecules (i.e., antigens) on the surfaces of microbes, like a key fitting into a lock.

“Every time you have any spatial interactions between things that are not completely squishy, the orientation of the binding partners is crucial for them to interact with each other,” explained Kate Adamala, Ph.D., an associate professor of genetics, cell biology and development at the University of Minnesota. “It would be difficult to imagine evolution of any effective biological binding if there wasn’t this pre-agreed [upon] system of chirality.”

Each biological molecule generally exists in a single configuration. However, scientists are increasingly able to generate mirror versions of those molecules in the lab, some of which have practical purposes. For instance, whereas natural-chiral molecules are subject to speedy degradation by cellular enzymes, their mirrors are not, prompting researchers to explore how to use these mirror molecules (e.g., peptides) as therapeutics that last longer in the body.

Such innovation paves the way for a new possibility: mirror organisms, comprised entirely of molecules with the opposite configuration to life as we know it—and bacteria represent a key first target. Generating mirror bacteria is not currently possible and wouldn’t be for at least a decade, if not longer, according to Adamala and her co-authors of an extensive technical report assessing the feasibility and potential risks of building mirror bacteria. Instead, the scientists ultimately conclude that mirror bacteria are best left in the realm of possibility.

Making mirror microbes

Experimentally flip-flopping the chirality of a bacterial cell feels a little like a niche prank. Why do such a thing at all? The answer leads to another question most people have pondered at one point or another: what is life?

While mirror bacteria would look like their naturally chiral brethren, in many ways they’d be completely alien. They could help determine if the tree of life once sprouted branches of opposite chirality.

“This is a deep ‘what if’ question,” said Vaughn Cooper, Ph.D., ASM President-Elect and a professor of microbiology and molecular genetics at the University of Pittsburgh. “Does the bias that we have on Earth exist because of some sort of intrinsic benefit to that combination of molecules, or is it just a frozen accident?”

There are other motivations for mirror cells as well. Extant life forms only recognize the natural conformation of molecules on bacteria—the mirror versions would be invisible to them. Predators that normally attack bacteria, like phages or nematodes, would no longer be able to see and destroy their targets.

The sleuth-like nature of mirror bacteria could be useful in, for example, industrial fermentation, where phage contamination can be a costly setback. Mirror cells would also fly under the radar of immune cells and could serve as (or deliver) therapeutics in the body without causing unwanted reactions.

The risks of mirror life

Yet, it is for these same reasons that mirror bacteria pose a problem. “A self-replicating organism built from mirror components—one that’s capable of sustaining itself and multiplying in the wild—would likely be invisible to many of the processes nature has evolved that keep a species in check,” said John Glass, Ph.D., Director of the La Jolla Campus at the J. Craig Venter Institute.

He, along with Adamala, Cooper and 3 dozen other scientists working in the U.S., China, Singapore, Japan and Europe, co-authored the technical report and accompanying Science article arguing against generating mirror life.

The immune systems of people, animals, plants and insects recognize molecules with specific orientations. If those molecules were reflected, as they would be on mirror bacteria, immune recognition would be impaired and basic immune defenses could fail. It is known from existing immunodeficiencies that a muted immune response can be deadly.

“Just having a few chinks in your armor of being able to recognize microbes is enough to make even benign bacteria pathogens, because there’s just no host control of those populations,” Cooper noted.

With such universally blunted immunity, mirror bacteria could trigger widespread infections. Since most antibiotics (which are already iffy at combating existing bacteria) wouldn’t be effective against mirror bacteria, we’d need to develop brand new drugs, and there’s no guarantee they’d work.

Moreover, it is improbable such antibiotics could be made quickly and at the scale needed to combat a potential outbreak in humans alone, not to mention impossible to design drugs to protect all the diverse life forms potentially impacted by mirror bacteria.

Mapping a way forward

The fact that it is not currently possible to make mirror organisms creates an opportunity for preventive, rather than reactive, action.

“Before we start losing sleep, it’s important to note that the risks from mirror bacteria are not imminent,” said Jonathan Jones FRS, report co-author and a group leader at the Sainsbury Laboratory in the U.K.

The goal of recent publications and upcoming events and initiatives (e.g., the Mirror Biology Dialogues Fund is supporting several international meetings throughout 2025 and the ASM Microbe 2025 Science and Society Lecture, which spotlights emerging scientific breakthroughs and their broader implications, will focus on the benefits and risks of mirror life) is to spark discussion across research, industry, government and non-governmental sectors.

Questions like “what research activities are the most risky and how do we monitor them?” are on the table. Mirror biomolecules are not inherently problematic—but technologies that facilitate self-replication, a key trait of bacteria, could be. Weiwen Zhang, Ph.D., Baiyang Chair Professor of Tianjin University in China, noted that coming together to discuss the risks now can prevent technologies from reaching that point.

Indeed, at the recent Asilomar conference on the future of biotechnology, there was broad agreement among the scientists in attendance about the need to develop regulations for mirror life research, and that the risks of creating mirror bacteria outweigh the benefits.

Moving forward, Adamala emphasized the continued need for cross-disciplinary communication. As 1 of 4 principal investigators on the only funded grant on mirror cells, she and her colleagues are now co-authors on the report advising against the very work they were once pursuing. It was after sitting down with ecologists, immunologists and researchers to discuss mirror bacteria that the team grasped the potential risks.

Adamala highlighted that these discussions, and the report and activities that emerged from them, can and should inspire similar reflective, community-driven discussions in other research areas, too.

Cooper agreed. “This represents an outstanding example of how much can be done when a group of scientists work together.”