...and old lace, yes

[gfish]

Like every starry-eyed geek, I had been waiting to see what NASA's big announcement yesterday was going to be. Given the background of the one researcher who had been listed, I was hoping it was going to be about abiogensis: the origin of cellular life. We still have very little idea exactly how you go from an enriched soup of organic elements and random amino acids to a working, self-replicating organism. If we're reading the geological history of the Earth correctly, it seems to have happened very quickly (in geological terms, i.e., a couple million years) after conditions had settled down enough to allow life. (Which suggests it might even have happened several times, only to be wiped out by the next massive collision as the early Solar System cleaned itself up. The "heavy bombardment" period was fun times!) But as far as we can tell, all life today is descended from a single genesis event, unless you had multiple ones with the exact same biochemistry, or ones close enough that they could merge somehow. Fairly unlikely, most would say.

Truth is, though, we have little data from which to determine the probabilities of any of this. If someone had come up with a new model for how it might have happened, that would be really cool. Or, better yet, a laboratory demonstration for some step in the process! There haven't been any big breakthroughs in that field since the Miller-Urey experiment -- and probably won't be. We're talking about reactions happening once or twice over literally millions of years in literally an ocean's worth of material. Maybe some magical quantum computer will eventually let us simulate that, but I'm not holding my breath.

So when Gizmodo claimed that a new form of life which used arsenic instead of phosphorous had been discovered, that was really, really exciting. There is a minor branch of exobiology looking for descendants of other genesis events here on Earth. The thinking normally is that even if there had been other trees of life, they would be extinct as our current one won out long ago. If any would be surviving, it would be in places that would be hostile to our form of life but not to theirs. We keep finding more and more extreme extremophiles, so it's not completely unreasonable to think that in some hellish corner of the Earth there might be a colony of what would be in every practical sense alien life. Which could tell us all kinds of things about really alien life someplace else. (It might even have come from someplace else. We might have come from someplace else. Earth and Mars trade meteorites regularly, and would have even more frequently back in the day. Which would be neat, but not very significant. Xenospermia doesn't explain how life started, after all, anymore than blaming it on a god does.)

And As+/P- life wouldn't be a complete surprise -- arsenic and phosphorous are very similar, chemically. Cells can't tell the difference between arsenate (AsO⁴) and phosphate (PO⁴), which would be fine except that when you use arsenate to turn sugars into usable energy, they form unstable compounds that quickly hydrolyze, preventing the ATP from being formed. Arsenic is poisonous, right? Now you know why. We already knew of extremophiles that could handle far more arsenic than normal. But they just handled the waste products better, preventing ATP production from breaking down completely in the presence of arsenic. Bacteria that were built from arsenic from the ground up would be crazy cool.

Unfortunately, of course, that's not what the announcement was. By taking extremophiles that could already handle hypersaline, hyperalkaline, high arsenic conditions, researchers found a strain that could not only tolerate arsenic but use it, incorporating it into their cellular structures -- including their DNA. (Except it's technically not quite DNA any more, just a very very close analog.) They don't need arsenic, they don't even prefer arsenic. They grow much faster and better with phosphorous. They're just a weird, interesting branch of normal life that can kind of survive if forced to use arsenic. Like if you were trapped in an airport and had to survive on Cinnabons and Dan Brown novels. You could do it, but it would suck and you probably wouldn't live as long.

Overall, this is certainly very cool, just not as cool as I was hoping. It still has exobiological implications, though. At its most basic, it expands the range of environments in which one might find life. More importantly, it proves that our specific biochemistry isn't the only one that works. Granted, this other one is almost indistinguishably close, but until now there was no evidence that any others were possible. You'll have to find a epistomologist for a more rigorous opinion, but it seems like many given two is more likely than two given one. So here's hoping.

Comments

[ladyaraia.livejournal.com]

Like if you were trapped in an airport and had to survive on Cinnabons and Dan Brown novels. You could do it, but it would suck and you probably wouldn't live as long.

Best analogy ever!

[tereshkova2001.livejournal.com]

Chemistry prof sez: AsO₄^3- and PO₄^3-
That loss of ATP through decomposition rather than ester formation is only one way in which arsenic is toxic. That's how arsenate ion is poisonous, but arsenic the metal is found in other forms as well (trivalent AsX₃ compounds, mostly) which inhibit a key enzyme in the citric acid cycle (or Krebs cycle if you're old school).

[randomdreams.livejournal.com]

Interestingly, I've read reviews (haven't had time to read the original source) that claim they have evidence there's substitution within ATP, meaning ATAs -- and a triarsenate is significantly weirder than a P/As point sub in DNA.

[tereshkova2001.livejournal.com]

Wait, what? Point me at those reviews/links to the originals?

[randomdreams.livejournal.com]

I'll see what I can find, but right now it's mostly commentary on the second slashdot.org article about it.

[randomdreams.livejournal.com]

commenter says "It wasn't phosphorus free, in fact they hadn't confirmed how much of the phosphorus had been substituted with arsenic, but they did mentioned it was not 100%. They also mentioned it was more than just DNA (ATP was also mentioned, although they implied more)."
But no citation given, and I haven't found any ref to support this, though I haven't gotten a chance to look deeply yet.

[tereshkova2001.livejournal.com]

That's about what I'd gathered from the Slashdot site. Interesting to watch, but not really useful information.

[randomdreams.livejournal.com]

Okay, I'm getting more dubious. Here's the Science abstract:
http://www.sciencemag.org/content/early/2010/12/01/science.1197258.abstract
Implies other places than DNA but doesn't say it.
The Astrobiology article:
http://www.astrobio.net/exclusive/3698/thriving-on-arsenic
Which talks about DNA recovery techniques only.
It's possible there was some material covered in the video, but because I'm a cheap curmudgeon my computer won't play their fancy video stuff. Hence lots of dubiosity from this quarter.

[gfish.livejournal.com]

Old school Krebs!

Thank you for the correction, I admit I'm stomping around where I only have a general science background at best.

[peteralway.livejournal.com]

Yeah, this is pretty much my take on the story.

[randomdreams.livejournal.com]

I've been yelling for a bit about "Power, Sex, Suicide: Mitochondria And The Meaning Of Life" by Nick Lane. One of the things he discusses is biogenesis, how he thinks it happened, and what residual evidence there is of his proposed mechanism. It's a seriously good book.

[sistawendy.livejournal.com]

We still have very little idea exactly how you go from an enriched soup of organic elements and random amino acids to a working, self-replicating organism.

Even a few million years is plenty of time for some fantastically weird stuff to happen near the triple point of water.

Something that nobody seems to bring up is the relative abundances of various elements. There's about a thousand times more P in the universe than there is As. Yes, this finding widens the scope of the variety environments that we should look at for life, but the ones we've got handy are still the most plausible.

And you mentioned that living on Cinnabons As would suck, and I bet you're right. How much more does it suck if you're multi-cellular? My guess, judging from the lack of enthusiasm the bugs have shown for As, is a lot.

[randomdreams.livejournal.com]

As has lower bond strength so it's likely to be a lot less stable long-term. But beyond that, I'm thinking it'd be very hard to form eukaryotic cells because you need a fairly good match between the host and the proto-mitochondria (I'm making the assumption that mitochondria started as parasites, rather than as ingested-but-not-digested food) for both to survive, so having one chock full of arsenic is going to make matching more difficult. A significant number of people are arguing that the prokaryote-eukaryote transition is more unlikely and difficult than the primordial soup-bacteria transition, leading me to imagine a universe of bacteria-filled planets with very few organized multicellular lifeforms.

[sistawendy.livejournal.com]

A significant number of people are arguing that the prokaryote-eukaryote transition is more unlikely and difficult than the primordial soup-bacteria transition, leading me to imagine a universe of bacteria-filled planets with very few organized multicellular lifeforms.

Well, duh. Bacteria, including the blue-green kind, ruled this planet for all but the last billion of its four-plus billion years. And what's evidence for the timing of the eukaryote transition? A decline in the number and variety of stromatolites.

[ilmarinen.livejournal.com]

Really? It seems that once you have life, of any type, doing it's life-thing with natural selection, etc., that creating variations of all sorts on that theme are just a matter of time. (And we have lots of evidence of life diversifying in all sorts of odd ways many different times.)

Whereas, getting the first actuallly self-replicating bit of living matter is that "lucky" moment bit.

-B.

[gfish.livejournal.com]

I share the intuition, but that just isn't what the geological record seems to indicate. Single cell life appeared really quickly, and then took 2 billion years to get eukaryotes, and another billion after that for multi-cellular life forms.

[ilmarinen.livejournal.com]

Yeah, but we have no evidence that the single-cell life arose more than *once*, correct? If it only happens once, then rapidly expands across the planet, seems that doesn't really support any arguments for how likely or unlikely it is to happen?

But then, of course, lots of opportunities for multi-cellular life to arise after that and it takes a lot time.

-B.