https://www.science.org/content/blog-post/mirror-life-worries

I wrote here a few years ago about the idea of completely enantiomeric “mirror proteins”, in the context of how they could benefit crystallography. These of course are made up of mirror-image enantiomers of the individual amino acids, but are otherwise the same (and cannot be differentiated by “non-chiral” means - they have the same molecular weights and other large-scale properties).

There’s been more talk (and worry) in the last few years about the possibility of extending this idea to mirror nucleic acids, mirror carbohydrates, on and on to the idea of making an enantiomeric living cell: “mirror life”. That would be a mighty ambitious thing to try, but it also could carry some risks that are unlike anything we’ve had to think about before. Here’s an article from 2024 on this, and there’s a detailed accompanying report on the idea of making mirror-bacteria. Just recently, Nature has highlighted a conference in Manchester on this same topic, and published this editorial from one of the researchers in the field.

As those stories indicate, no one is even close to making such things. But there are plenty of model systems along the way, and the question is where the potential dangers of this sort of work start to outweigh the scientific benefits. So let’s talk about both of those briefly. One outstanding question (for well over a century now) is why all life on Earth uses the same “handedness” of the chiral biomolecules (carbohydrates, amino acids and their associated proteins, etc.) One immediate answer is because all life on Earth stems from a common ancestor that used these, and that is almost certainly correct (albeit extremely hard to prove!) But that just leads to another question: why these ones and not the mirror images?

There seems to be no a priori reason, and indeed, in abiotic samples like carbonaceous meteorites we find both enantiomers of such compounds. There have been many rather esoteric physics-based proposals on how one enantiomeric series might be slightly more stable than another (and thus increasing its chemical odds) but none of these are even close to definitive. So was this an accident? If so, if there are living creatures using vaguely similar biochemistry on other worlds, are they broadly distributed half-and-half, or what? You open up a lot of tricky origin-of-life questions with these lines of inquiry, and mirror-image cells (or simply mirror-image models of them) could be a way to answer them.

On the downside, we don’t really know how our immune systems might respond to complex mirror-image biomolecules. They might just slide by invisibly, but they might well not - after all, there are a lot of ways to do molecular recognition. Moving past that, could a mirror-image cell survive in the wild? No one’s sure: if it has enough intracellular machinery to make its own key constituents, it could probably use the achiral building blocks that are lying around everywhere and keep going with them. And a big problem with that is that something like an enantio-bacterium would presumably have no natural enemies, and would presumably be nonresponsive to antibiotics and other defenses that bacteria use to keep each other in line. So the possible downsides are rather large - but no one knows how possible they are.

I doubt if anyone is interested in my own take, but for what it’s worth I think that we are sufficiently far from producing any actual organisms that I am not worried about this research. But I think it is prudent to think about what could eventually happen, and perhaps set some tripwires for the future. For now, though, I think that this is interesting and challenging research, and I think it should go on.

https://www.science.org/content/blog-post/mirror-life-worries