[roenxi]

Doesn't sound very scary on the face of it. Apparently [0] the problem with Thalidomide was that the chirality could spontaneously reverse, so that sort of thing must happen frequently in nature. If bacteria haven't figured out how to use mirroring under evolutionary pressure it probably doesn't actually have any advantages over following the herd.

[0] https://en.wikipedia.org/wiki/Homochirality#In_biology

[jefftk]

> that sort of thing must happen frequently in nature

Individual chiral molecules can happen naturally, sure, but not entire organisms. From the report: In a mirror bacterium, all of the chiral molecules of existing bacteria—proteins, nucleic acids, and metabolites—are replaced by their mirror images.

In the fitness landscape there is an absolutely enormous gulf between standard and mirror bacteria, large enough that no amount of incremental evolutionary pressure could flip the ~billion chiral bonds in a given bacterium simultaneously.

[roenxi]

Nature has built a lot of bacteria over the millennia. It probably has experimented with just building the whole thing backwards.

That sounds simpler to do than, say, evolving a cogwheel (which does happen occasionally) or actually developing some of these molecules in the first place. It'd be weird for evolution to struggle so much on trying such a simple concept somewhere. This is a process that naturally figured out solar power, a bunch of mechanical engineering properties, various chemical techniques, all sort of fluid dynamics and statics, radiation resistance, sensing and control systems, etc, etc. If it doesn't build things backwards, more likely than not it is because it doesn't work well. The process knows how to do quite complex engineering tasks.

[jefftk]

> It'd be weird for evolution to struggle so much on trying such a simple concept somewhere.

While "building it backwards" sounds simple to us, it's not simple at all in evolutionary space. Evolution operates over a fitness landscape, where every configuration of an organism has some fitness (essentially, probability of reproducing). It can make good progress as long as there are paths that don't require traversing areas of impractically low fitness. The problem in this case is that between "normal" and "mirror" is an area of absurdly low fitness, which evolution shouldn't be expected to be able to cross.

[roenxi]

We can't really say what is hard, because evolution tends to be more creative than anyone expects. But we can say it sounds easy - evolution would only need to come up with a "build this with reverse the chirality" mechanism and run everything through it. That'd even be what humans are doing in this research, I suspect. If there are advantages to reversing chirality then there'd be lots of paths where partially reversing chirality of parts of an organism would be interesting or creating clouds of reverse-chirality molecules would be evolutionary powerful.

It wouldn't be likely, but we're talking millions of years and a process that has overcome some remarkable engineering challenges. Finding one place where building backwards then extending that just wouldn't be such a big deal.

[notfed]

I think the ostensibly scary subject here is mirror DNA or RNA, not anything-that-doesn't-self-replicate.

> If bacteria haven't figured out how to use mirroring

It's unclear bacteria have ever "attempted" it. The synthesis of DNA is incredibly intricate and complex, and the set of proteins that do it are believed only to have ever evolved once. In order for a bacteria to have "attempted" this, it would have to evolve an entirely new set of proteins from scratch.

Personally I think a self-replicating photosynthetic cell with mirror DNA is as scary as self-replicating photosynthetic plastic.

[Aerroon]

>It's unclear bacteria have ever "attempted" it.

They have: https://pubmed.ncbi.nlm.nih.gov/24647559/

[Filligree]

> self-replicating photosynthetic plastic

Cellulose? It did cause quite the stir, I'll grant you.

[aydyn]

What's scary about mirrored DNA? DNA is information store proteins are actuators.

> would have to evolve an entirely new set of proteins from scratch.

Mirrored amino acids already exist in some organisms.

[notfed]

> What's scary about mirrored DNA

Exponential growth of a self-replicating cell with zero predators.

> Mirrored amino acids already exist in some organisms.

You can have an entire planet full of mirror amino acids if you want; that's not the hard part. The hard part is evolving the entire set of mirror transcription proteins.

[aydyn]

Where are you getting exponential growth without predators? That simply does not follow logically from any assumptions.

[kstrauser]

There are all kinds of examples of where the isomers of common compounds are bad for you, i.e. https://www.sciencealert.com/some-drugs-have-mirror-image-ch...

[jmward01]

My go-to with any 'thing x could wipe out everything or is better than everything' is exactly this. If nature hasn't found it then I don't worry as much. That doesn't mean this shouldn't be considered and studied carefully, but this sounds like a bit more fear than it likely deserves.