A new end-the-world scenario: Photosynthetic Mirror Cells | Hacker News Reader

A new end-the-world scenario: Photosynthetic Mirror Cells

overcomingbias.com

18 pointsstcredzero27 comments

The end-the-world scenario is this: A droplet of photosynthetic cyanobacteria escapes into the wild. Since they are immune to natural predators, they take over the niches of oceanic photosynthetic organisms, converting more and more of the planet's photosynthetic biomass to inedible mirror-life. Since ocean photosynthesizes are at the foundation of so many food webs, many ecosystems crash, civilization falls, homo sapiens goes extinct.

Eventually, something will evolve to eat the mirror-life, but by then we'll all be dead.

I'm not buying the idea that simply having mirrored proteins is enough of an advantage for an organism that it would be able to completely out-compete the majority of already existing natural organisms.

I agree. It would seem to me that if such organisms had such a big advantage in the wild they should have already evolved independently.

Note though, this would be really hard to evolve. As an analogy, the photosynthetic center RuBisCO is fairly wasteful, so any organism that can improve on RuBisCO would have a huge advantage. Only problem is RuBisCO is not easily evolvable (like brittle code), thus we don't know of any improvements although they are quite possible theoretically.

Evolution doesn't seek out advantages, it just happens statistically that changes which carry advantages have more probability of rising to fixation within a species. Plus as ptpu touched on (and I'd wager he's more knowledgeable than I am) it's probably hard to even get the necessary mutations let alone having them stick around, or the species lasting long enough, etc.

By having mirrored proteins and sugars, such organisms would have no predators or parasites. This condition -- having no natural predators and parasites -- has been replicated many times through the dislocation of species through human transport. Often the result is that such a species is at a huge advantage, much to the detriment of the environment. These are called "Invasive Species." (Asian Carp, anyone? Brown Snakes in Hawaii? Kudzu? Rabbits in Australia?)

Mirrored proteins and sugars would be much worse, since it would be exceedingly hard to evolve an ability to decompose these. I imagine that would happen eventually, but it would take such a long time, our environment would be in shambles and we'd be all long dead.

perhaps I'm just showing my ignorance, but I don't know any examples of invasive bacteria to trust that they'd be a problem in the same way, afaik predator/prey/competition is way more complicated at the micro level.

but I don't know any examples of invasive bacteria to trust that they'd be a problem in the same way

Actually, that makes this even more dangerous. Normally there isn't much scope for invasive species of bacteria precisely because they've been around for a very long time and because they're everywhere. Odds are something has already evolved to eat something else that's similar. Mirror proteins break this. All of a sudden, nothing can eat these new organisms and survive for very long. It would be something unprecedented.

I think evolutionary humility is a great thing to be reminded of, thank you Palomides.

What's interesting to me is, an organism wouldn't have to out-compete the majority of already existing natural organisms to end the world, it "only" need replace the base of the ocean ecosystem. If a new form of bacteria killed all of the krill and plankton it would surely have grave consequences.

This should be trivially fixable. Nobody wants such an eventuality to occur, so the smart money is on wiring in a dependency on some externally supplied, scarce element; for example, ensure that one or more of the enzymes involved in mitosis require a supply of a rare earth element or a purely synthetic (non-biosynthetic, non-natural) organic molecule as a cofactor.

How about this as a scenario: Such safety mechanisms are engineered at first. A rare earth element is used as the cofactor. After a number of years, an organic cofactor is introduced and becomes widely adopted by industry as it reduces costs. Since this works so well, industry becomes cavalier about the release of such organisms, as they all soon die anyways.

A rogue bioengineer creates an artificial organism that can produce the cofactor. Hilarity ensues.

Even if predators can't metabolize the mirror molecules, they can still eat them (possibly dying afterwards). So you'd need to release the mirror algae( ?) in very large quantities for them to overcome the predatory pressures in their environment.

It also means that by killing predators (zoo-plankton), mirror algae are creating a niche for standard algae too. So you could end up with a soup of R and L life, but diminished predatory activity.

There would be evolutionary pressure for the predators to be able to distinguish the mirror algae and not eat them. Such predators would undoubtedly arise, which would give mirror-algae an evolutionary advantage.

Mirror-algae would only have to be released in large enough quantities to gain a toehold.

It's not like viruses and antibiotics are the only thing keeping OTHER cells from taking over the planet - which seems to be the crux of the conjecture.

I call shenanigans.

Sweet Jesus! Scientists have discovered gravity! In addition, to add insult to injury, as things get closer they only increase the gravity between them. Soon, the world will collapse into a swirling singularity if we don't take swift, immediate action. Refrain from forming crowds. Be cautious not to marry your dinner service. Only you can prevent black holes.

/sarcasm

The reasoning of this article is incredibly specious. There is no adequate evidence or inference that mirror cells would have any advantages over standard life forms. Isomers aren't incredibly divergent structures that nature fails to handle on a massive scale. Isometric molecules are a basic part of molecular life. Mirror cells would have the same biotic survivorship of the rest of the cells on the planet.

By synthesizing cells that use a proportion of molecules that have an inverse chirality to the majority of biotic life we're not exactly making cancer airborne and contagious.

They wouldn't have an inherently higher survivorship, but it would be toxic to predators, wiping them out (either directly by toxicity, or indirectly by starvation), at the same time as growing and spreading further. Natural evolution itself is unlikely to develop an organism capable of metabolizing mirror sugars, fats, proteins.

So this means people have to take an active role in eradicating this life form, if it ever comes to be.

Maybe someone with industrial chemistry experience can explain this to me- if an organism contains both normal and "mirror" ribosomes, it should produce both isomers of a given protein. How do you separate the mirror versions from the normal versions on a large scale?

Isomers do tend to act differently in certain situations. You can't shake someone's left hand easily with your right. Although I'm not certain on the exact mechanisms I believe it is possible to screen molecules of different chiralitites by using chemicals that only attach to a right hand or a left hand partner. They might also pass through mazes and filters in different directions.

It's a good question, and I'd love to hear a detailed answer.

Yes, there are many ways to make isomers--it is done commonly in the pharmaceutical industry. Can be done directly via synthesis, or a racemic mix can be separated by physical processes such as crystalization or enzymatically. Most enzymes have a chirality (like the glove analogy), so they tend to create produces with a single isomer.

This said, making an organism with mixed chirality would likely not be effective because, likely, many reactions would not proceed or would proceed with poor efficiency. All D- or all L- would work fine, but any evolved organism would suffer/die with a mix of D- and L-.

There are ways of separating individual enantiomers from a racemic mixture of both. For example, crystallization will create separate crystals of each (this is how it was done first by Pasteur).

Relevant resource on the topic: http://en.wikipedia.org/wiki/Chirality_(chemistry)

What is a mirror cell?

A cell constructed entirely from molecules with complementary chirality[1] to that of the molecules in normal life on earth. Alternately, read the article:

  A life-form … based on mirror-image versions of earthly
  proteins and DNA.

[1]http://en.wikipedia.org/wiki/Chirality_(chemistry)

I think it is supposed to mean a cell in which the amino acids have D chirality (as opposed to the more common L amino acids); the fully 'mirrored' cell the link is suggesting doesn't seem fully thought out.

If this comes to fruition, we can at least console ourselves that Global Warming would be stopped (by killing out ocean-borne oxygen breathers).

But really, just how much of organisms constitutes molecules that can be mirrored? And whether or not a lion's stomach can actually extract nutrients from a dead mirror gazelle, the mirror gazelle is still very dead. Even if it wasn't ripped apart, stomach acid is unconcerned with what 'handed-ness' a molecule is.

Recently it was proven possible to construct an organism through synthetic processes. This is still limited to very close copies of the real things, but could be adapted to produce reverse chiral molecules.

http://www.jcvi.org/cms/press/press-releases/full-text/artic...

Edit: Although, the added difficulty would be the need to reconstruct a cell completely out of mirror molecules for it to work. In the case above, the genome was injected into an existing cell and left to replicate. So it's not quite a trivial thing to do.

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