What is ‘mirror life’ and why have scientists opposed it?

In a mirror, left and right become swapped. While you unscrew a bottle cap anti-clockwise in the real world, in the mirror you’ll be rotating it clockwise. Anything that has a handedness -- left or right -- is said to be chiral.

Chiral molecules that are mirror images of each other are called enantiomers. A good example is the compound thalidomide. It was sold as a sedative for four years in the late 1950s before being withdrawn. Scientists found that the right-handed enantiomer worked as a sedative but the left-handed one caused severe birth defects.

In the human body itself, the amino acids used to make proteins are all left-handed. Their right-handed enantiomers are absent. Similarly, the DNA in all our bodies is right-handed (the double-helix twists to the right). The reasons are a mystery.

Scientists have been making and studying enantiomers in the lab for a long time, but recently a few of them have started on the road to creating ‘mirror microbes’ -- synthetic bacteria whose building blocks are enantiomers of their natural counterparts.

Earlier this month, an international group of scientists, including Deepa Agashe of the National Centre for Biological Sciences, Bengaluru, published a 300-page technical report and a commentary in the journal Science warning against efforts to build mirror life.

“Life isn’t even-handed: many cellular components are all either left or right handed. But we are now (uncomfortably) close to being able to make flipped “mirror” cells,” Dr. Agashe wrote on X (Twitter) on December 13.

“Our analysis suggests that mirror bacteria would likely evade many immune mechanisms mediated by chiral molecules, potentially causing lethal infection in humans, animals, and plants,” the commentary read. “They are likely to evade predation from natural ... and many other predators, facilitating spread in the environment.”

They acknowledged that mirror microbes may have valuable applications. For example, industrial facilities that use bacteria for decomposition or fermentation or to speed up chemical reactions could substitute them with mirror bacteria, which are likely to be more resilient. But the researchers also say the cons outweigh the pros in their analysis, and that there are other ways to solve the problems mirror bacteria can while incurring less risk.

“Countermeasures such as mirror antibiotics, crops engineered to be resistant to mirror bacteria, and mirror phages appear very unlikely to be sufficient to stop or reverse the spread of mirror bacteria throughout global ecosystems or to prevent unacceptable loss of life and irreversible ecological changes that could result,” they added.

“The primary challenge with these countermeasures is our inability to deploy them throughout the ecosphere at sufficient scale to prevent or counter dissemination and evolutionary diversification of mirror bacteria in the wild. They could therefore only protect against a fraction of the potentially immense harm.”

The team has invited other researchers to examine their evidence and arguments and conduct more studies to better quantify the risks mirror life may pose.