

A new end-the-world scenario: Photosynthetic Mirror Cells - stcredzero
http://www.overcomingbias.com/2010/12/ban-mirror-cells.html

======
stcredzero
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.

~~~
Palomides
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.

~~~
splat
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.

~~~
Jach
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.

------
iwr
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.

~~~
stcredzero
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.

------
dedward
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.

------
Gianteye
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.

~~~
iwr
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.

------
RodgerTheGreat
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?

~~~
Gianteye
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.

~~~
ptpu
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-.

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

------
tree_of_item
What is a mirror cell?

~~~
RodgerTheGreat
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)>

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

------
sliverstorm
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.

~~~
iwr
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...](http://www.jcvi.org/cms/press/press-releases/full-
text/article/first-self-replicating-synthetic-bacterial-cell-constructed-by-j-
craig-venter-institute-researcher/)

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.

