≡ Menu

Arsenic and Odd Life

As if it were news, one thing the great flap over astrobiology and yesterday afternoon’s NASA news conference tells us is that anything smacking of extraterrestrial life brings over the top commentary long before the findings are officially discussed, as should be clear from some of the Internet blogging about the GFAJ-1 bacterium found in Mono Lake. And what a shame. Despite the astrobiology teaser, GFAJ-1 does not in itself tell us anything about alien life and does not necessarily represent a ‘shadow biosphere,’ a second startup of life on Earth that indicates life launches in any available niche. But the find is remarkable in its own right.

Let’s leave the astrobiology aside for the moment and simply focus on the fact that life is fantastically adaptable in terms of biochemistry, and can pull off surprises at every turn. That’s always a result worth trumpeting, even if it leaves the wilder press speculations in the dust. After all, it’s long been assumed that the six elements that underlay the basic chemistry of life are carbon, hydrogen, oxygen, nitrogen, phosphorus and sulfur. Despite persistent speculation, few thought life could exist without them.

Now we learn that the GFAJ-1 bacterium found in eastern California’s Mono Lake can, at least in the conditions of a fascinating experiment, use arsenic in its metabolism rather than being poisoned by it. Arsenic occurs in the lake in one of the highest concentrations of any site in the world. Let me quote the ever reliable Caleb Scharf (Columbia University) on arsenic and its role:

Arsenic is an insidious element. With 5 outer valence electrons the arsenic atom is chemically similar to the biologically critical element phosphorus, but only in crude terms. Life depends extensively on phosphorus – it helps form the molecular backbone of DNA, it is part of molecules like Adenosine triphosphate (ATP) that serves as a vital rechargeable chemical battery within all living cells, as well as many other biologically vital roles. Arsenic on the other hand can weasel its way in, waving its valence electrons in a come-hither fashion, and getting the best seat in the house. The problem is that once an organism takes in arsenic, replacing some of its phosphorus, it typically begins to malfunction – arsenic is is a fatter atom and biochemistry is a sensitive thing. There is good reason why arsenic has long been a poison of choice for nefarious human dealings.

Indeed. GFAJ-1 is intriguing because rather than just being tolerant of a toxin like arsenic, it’s actually able to use it. The team working under Felisa Wolfe-Simon (USGS) reported online today in Science that phosphorus is here replaced by arsenic, a case of an alternate building block for life of the kind long speculated about by science fiction writers. This from Nature:

Arsenic is positioned just below phosphorus in the periodic table, and the two elements can play a similar role in chemical reactions. For example, the arsenate ion, AsO43-, has the same tetrahedral structure and bonding sites as phosphate. It is so similar that it can get inside cells by hijacking phosphate’s transport mechanism, contributing to arsenic’s high toxicity to most organisms.

The team proceeded by collecting mud from the lake and adding samples to a salt medium that was high in arsenate, then diluting the material to wash out remaining phosphate. Steeping the cells in arsenic, the scientists discovered an organism that seemed to grow well under these conditions, even after multiple generations since their first collection more than a year ago. What phosphorus was available to the bacteria was present only in traces from the original colony of cells, and in impurities found in the growth medium. Again from Nature:

When the researchers added radio-labelled arsenate to the solution to track its distribution, they found that arsenic was present in the cellular fractions containing the bacterium’s proteins, lipids and metabolites such as ATP and glucose, as well as in the nucleic acids that made up its DNA and RNA. The amounts of arsenate detected were similar to those expected of phosphate in normal cell biochemistry, suggesting that the compound was being used in the same way by the cell.

Can these bacteria replace phosphate with arsenic naturally? Wolfe-Simon herself says thirty years of work remain to figure out exactly what’s going on, a comment on the preliminary nature of this work, which remains controversial in some quarters and is in obvious need of extensive follow-up. No shadow biosphere yet, but obviously the quest is ongoing because of its implications, and we’ve now received one very tantalizing piece of evidence that such things may be possible.

If life really did start here more than once — a finding that is not remotely demonstrated by this work — then we can talk about how likely it will have done the same thing on distant planets, upping the chances that we live in a universe where life emerges whenever given the chance. But we’re hardly there yet, as became evident in the exchanges between Wolfe-Simon and Steven Benner (Foundation for Applied Molecular Evolution) at the news conference. British science writer Ed Yong fleshes out some of the reasons for skepticism:

It’s an amazing result, but even here, there is room for doubt. As mentioned, Wolfe-Simon still found a smidgen of phosphorus in the bacteria by the end of the experiment. The levels were so low that the bacteria shouldn’t have been able to grow but it’s still not clear how important this phosphorus fraction is. Would the bacteria have genuinely been able to survive if there was no phosphorus at all?

Nor is it clear if the arsenic-based molecules are part of the bacteria’s natural portfolio. Bear in mind that Wolfe-Simon cultured these extreme microbes using ever-increasing levels of arsenic. In doing so, she might have artificially selected for bacteria that can use arsenic in place of phosphorus, causing the denizens of Mono Lake to evolve new abilities (or overplay existing ones) under the extreme conditions of the experiment.

And I should also return to Caleb Scharf, who notes that while phosphorus is relatively rare — in terms of cosmic abundance — compared to other major bio-chemically important elements, it is a thousand times more abundant than arsenic, which is little more than a trace by comparison. So much for the idea of entire biospheres crowded with life forms drawing on the stuff, at least in terms of the odds. The GFAJ-1 experiments make for a fascinating story, one that was upstaged by a media circus but remains notable news for all that. Paul Davies, one of the authors of the paper, calls this work ‘the beginning of what promises to be a whole new field of microbiology.’

But again, note the caveat, as Davies explains:

“This organism has dual capability. It can grow with either phosphorous or arsenic. That makes it very peculiar, though it falls short of being some form of truly ‘alien’ life belonging to a different tree of life with a separate origin. However, GFAJ-1 may be a pointer to even weirder organisms. The holy grail would be a microbe that contained no phosphorus at all.”

The paper is Wolfe-Simon et al., “A Bacterium That Can Grow by Using Arsenic Instead of Phosphorus,” published online by Science (2 December 2010). This article in Astrobiology Magazine provides an excellent backgrounder on the Wolfe-Simon team’s methods. Wolfe-Simon’s own Web site is impressive and well worth checking re her ongoing work.

tzf_img_post

Comments on this entry are closed.

  • Frank December 2, 2010, 18:48

    Interesting stuff. It points just how adaptable life can be.

  • andy December 2, 2010, 19:03

    Unfortunately not a genuine “shadow biosphere”, but certainly it indicates that life can do a whole bunch of really weird stuff. Makes me wonder what else is out there on our own planet, eking out a quiet existence in some remote and hostile corner of the world.

  • Ronald December 2, 2010, 19:22

    Yes, fascinating from a biological point of view, but not really with regard to the occurrence and abundance of life in the universe, since, as Kurt9 points out here:

    http://nextbigfuture.com/2010/12/bactera-made-with-arsenic-instead-of.html#disqus_thread

    Phosphorus is about 1000 times more abundant in our MW galaxy (and elsewhere?) than Arsenic.

    And it is still carbon and water based life, which is also logical.

  • kurt9 December 2, 2010, 19:37

    “And I should also return to Caleb Scharf, who notes that while phosphorus is relatively rare — in terms of cosmic abundance — compared to other major bio-chemically important elements, it is a thousand times more abundant than arsenic, which is little more than a trace by comparison. So much for the idea of entire biospheres crowded with life forms drawing on the stuff, at least in terms of the odds.”

    20 minutes of internet search told me this one. It also told me that the only other candidate for “alternative” life would be the replacement of Sulfur with Selenium. This is not bloody likely because, although Phosphorus is a 1000 times more common than Arsenic, Sulfur is 100,000 times for common than Selenium.

    Just look at the abundance of elements in the solar system, milky way galaxy, and their relative abundance based on stellar nucleosynthesis. Then look at the period table and look at where the most common elements are. There’s not much option left over for “alternative” life chemistry.

    Also, Oxygen is 5 times more plentiful than Nitrogen. This means that water is going to be 5 times more plentiful than Ammonia. So, even if there is life that lives in ammonia rather than water, its not going to be common compared to the life living in water. As for liquid Nitrogen, forget about it. Reaction rates are too slow at those kind of temperatures for any kind of life to have evolved.

    The most common life in the universe is going to be Carbon-based life that uses water as the solvent.

  • Bounty December 2, 2010, 19:46

    After listening to the NASA release, this article and a few others, I’m genuinely excited about Arsenic. Partially because I know so little about it. Apparently it can make anoxygenic photosynthesis work, replace (mostly) Phosphorous and it’s extra reactive for all those cold environments. Seems like we’ll be seeing more tests for it on our solar system missions.

  • Alex Tolley December 2, 2010, 21:30

    While on the face of it, this is quite remarkable, we need to put its strangeness in context. Some organisms have managed to replace phosphorus with sulphur in their membranes, and we can bioengineer organisms to use different translation codons and even 4 base codons. Life continually surprises us with its adaptability and apparent breaking of classic biological dogma.

    There should be reason for some skepticism about the results. Why doesn’t the DNA backbone fall apart with arsenic? Is there enough energy in the bonds to provide much metabolic energy? Is there some experimental error?
    For example, what if the bacterial growth is just using the available phosphorus, then the arsenic replaces it leaving a dying [fossil?] organism that is then analyzed are produces the result?

    Personally I was annoyed at Nasa making so much of this, titillating the press for what was a relatively small impact on astrobiology.

  • P December 2, 2010, 22:47

    “Personally I was annoyed at Nasa making so much of this, titillating the press for what was a relatively small impact on astrobiology.”

    FWIW I agree Alex. NASA and any other agency/institution in a similar situation is eventually going to have to change the way it announces things like this. What might have been appropriate in the 1960s simply wont do in a rampantly viral, socially networked world where daisy chains of Chinese whispers will corrupt code and fill ellipses in no time at all. Oh, and make the ‘major story’ the viral hype, not the research.

    Interesting discovery though!

    P

  • Gregory Benford December 3, 2010, 1:00

    True, Arsenic is rarer on average, or so we think from stellar abundances. That may imply such odds for planets, but that’s not clear.
    It’s an important result for what it opens. In low energy
    environments, such as those around the small red stars now found to be
    by far the majority in all galaxies, Arsenic might be preferred by
    local chemistry. This opens the window to life in such strange but
    common environments. I suspect chemistry allows life to make it way quite variously.

  • Doug M. December 3, 2010, 6:50

    “Also, Oxygen is 5 times more plentiful than Nitrogen. This means that water is going to be 5 times more plentiful than Ammonia.”

    This does not follow.

    Doug M.

  • Athena Andreadis December 3, 2010, 10:40

    From the results of the paper itself, it’s highly unlikely there’s a lot of arsenic in the DNA: almost all of the arsenic went into the organic phase (nucleic acids segregate into the aqueous phase) and the ratio of arsenic to phosphorus was a measly 7:1. NASA should remember the tale of the boy who cried wolf. My analysis: Arsenic and Odd Lace

  • Bill B. December 3, 2010, 11:35

    Either way you look at it, this is good news proving the resiliency of life all around, even if this idea of a ‘shadow biosphere’ proves unfounded.

    It is another piece of evidence to increase our confidence in finding life outside of the Earth’s biosphere(s).

  • Bill B. December 3, 2010, 11:45

    Today’s XKCD comic on “Arsenic-Based Life”:
    http://xkcd.com/829/

  • kurt9 December 3, 2010, 13:31

    This does not follow.

    Yes, it does. Water is H2o. Ammonia is NH3. Since Hydrogen is everywhere, the limiting element for water is Oxygen and ammonia is Nitrogen. Since Oxygen is more plentiful than Nitrogen, it makes sense that water will be more plentiful than Ammonia, which is what we see when we look at the outer solar system.

  • Mark Wakely December 3, 2010, 14:31

    The one thing they didn’t tell you was that the bacteria only grows in a medium of old lace. And how rare is that in the Universe?

  • Didac December 3, 2010, 14:40

    20 minutes of internet search told me this one. It also told me that the only other candidate for “alternative” life would be the replacement of Sulfur with Selenium. This is not bloody likely because, although Phosphorus is a 1000 times more common than Arsenic, Sulfur is 100,000 times for common than Selenium.

    However, selenium replacte the sulfur in cystein in the selenocystein aminoacid. But, as far as we know, no organism can thrive with a Se:S ratio of 5:1, and GFAJ-1 does with a As:P ratio of 5:1.

    Anyway, according to element distribution in the universe and in the planetary systems, CHONPS is the logical way.

  • Daniel December 3, 2010, 14:59

    Silicon it’s a much more common element on the planet Earth than Carbon, but ever that, life on Earth it’s Carbon-based life forms… but if we take kurt9 analogy of elements abundance for life,on Earth it’s supposed be planet of Silicon-based life form,BUT isn’t.
    so un my opinion it’s too early for we jump to conclusion that life it’s based on the element abundance in a planets or in the universe.
    i think that planet environment and condition cout first that the elements abundance
    maybe there isn’t Silicon-based life form on Earth because Earth hasn’t favorable environmental conditons for this kind of life… anyway just a speculation….

  • Bounty December 3, 2010, 15:03

    Ok some of the reasoning here seems a little short. Helium accounts for 24% of our galaxy, yet it’s rare on earth. Originally Oxygen was locked up in rocks here. Phosphorous and H2O had to get rained down on us by comets. Our configuration of rocky then giants may or may not be common. I wouldn’t automatically assume exoplanets are full of X or Y chemicals on the surface (or some particular habitable boundary, crust, mantle etc.) unless you have evidence. Also, because we’re the only sample of life we know of, doesn’t automagically make us the most common or prefered by nature. We may find out one day that red dwarfs in elliptical galaxies may have an uncanny way of making arsenic earths.

  • andy December 3, 2010, 16:27

    Also, Oxygen is 5 times more plentiful than Nitrogen. This means that water is going to be 5 times more plentiful than Ammonia.

    Sorry, but no. You also have to consider the stability of the molecules, the energetics of forming them, etc. (IIRC this kind of thing acts to make ammonia somewhat rarer, but the point still stands that chemistry is NOT just throwing a bunch of elements together in a randomised mix)

  • kurt9 December 3, 2010, 17:06

    …but if we take kurt9 analogy of elements abundance for life,on Earth it’s supposed be planet of Silicon-based life form,BUT isn’t.

    Its a combination of two factors. Life will use the most abundant elements (because evolution is based on probability) but will use only those elements whose chemistry works for biology. This is the reason why I do not expect to find life that is significantly different than our own.

    Athena’s analysis is what I suspected about this bacteria.

  • Zen Blade December 3, 2010, 18:35

    Hey folks,

    I would just add my voice to those who say, do not take much from this report (from Iron-lisa and colleagues). What they have shown is that the bacteria can survive in high levels of Arsenic. That’s about it.

    Beyond that… there are lots of open questions. The data are not particularly strong, and any hints of the arsenic being used in place of phosphorus is… dubious at this point. Yes, there are data that can be interpreted as such, but there are alternative explanations in some cases, and other cases the data are just puzzling. And other cases the experimental techniques used are beyond my comprehension (and many other scientists)… which means that there will be relatively few people who can properly evaluate each and every technique used in the paper… so, since I feel that some of the data, which I understand looks fishy, I feel even more suspicious about the parts of the paper that I can not properly evaluate.

    I am not saying that the authors’s conclusions will not be eventually reached. Only, that the data so far presented are not very strong. There are a number of alternative explanations for their observations. The paper itself is rather short, and the data are rather scarce. It is just way too premature to declare that this organism has evolved a proteins(s) that allow for the use of arsenic/arsenate in place of phosphorus/phosphate.

    That being said, it could very well be that this organism has achieved that which the authors claimed, but any scientist worth their PhD would not make such *bold* and *exceptional* claims given the paucity of data presented in this single paper.

    I shall refrain from commenting on the press conference and the circus-like atmosphere that really undermines the whole concept of science (other than what I just wrote).

    -Zen Blade

  • Michael Simmons December 4, 2010, 1:14

    Personally I find the paper referenced in the article linked below has having much more impact on the possibilities of life on other planets.

    http://www.newscientist.com/article/mg20827874.800-life-is-found-in-deepest-layer-of-earths-crust.html

    If life can survive at these depths. Maybe it can start there too.
    The conditions would be a lot more stable than on the surface.
    Potentially all rocky planets could have life start underground and move out as far as the environment allowed it.

  • Adam December 4, 2010, 1:32

    Hi All
    Rather than joining what seems to be a Gripe-Fest I’d like to suggest that water is preferable as a medium when it’s actually liquid. There’s a lot of the stuff in the Universe, true, but finding it in its liquid phase is pretty rare. More often we’ll find it mixed with ammonia since that lowers their mutual melting point significantly. On a moon/planet just a bit warmer than Titan there could be seas of such mixtures and I suspect such maybe quite common around stars cooler than ~4,900K, since UV levels decrease enough to allow ammonia to accumulate.

  • Procyan December 4, 2010, 1:49

    The idea that arsenic-DNA, arseno-lipid membranes and all the myriad normally phosphorus-bearing molecules function together to support biological function is astounding. It is very very very not likely to be borne out as reputable labs seek to replicate, verify and extend this work as the originating authors should have prior to this silly “cold-fusion” redux. Instead of too many neutrons we have too little phosphorus.

    Moreover, that whole presentation was weird. What were they selling and to whom?

  • Jamie December 4, 2010, 12:58

    I’m a bit wound up about this story. Granted, my biochemistry is a bit rusty, but something about this stinks to high heaven. Since when do we start having news conferences before independent verification? It’s a tad depressing to me, that NASA has sunk to this. I thought the entire presentation was…strange.

    I very much enjoy your website, Paul.

  • Ronald December 4, 2010, 20:58

    Adam: “I’d like to suggest that water is preferable as a medium when it’s actually liquid. There’s a lot of the stuff in the Universe, true, but finding it in its liquid phase is pretty rare.”

    I fully agree, which means we are back to the Habitable Zone concept as defined by Kasting et al.

  • Eniac December 5, 2010, 1:15

    Athena, you write yourself that their final isolate had 11% arsenic in the DNA. If that is true, how is it possible that the arsenic is not actually functioning like phosphorus in DNA? Surely it is impossible for DNA to work if 11% of it is non-functional, therefore the parts with arsenic must be functioning, therefore it is quite conceivable that 100% arsenic-DNA could also function.

    I would not call a 7:1 ratio of arsenic to phosphorus “measly”, by a long shot. Like Procyan, I find it absolutely astonishing. Either there is something wrong with the experiment, or the organism has indeed adapted to the difference between phosphorus and arsenic in all of its uses of phosphorus. If the latter, I do not see how 100% would be any more astonishing than 11% or 7:1 (88%) already is.

  • Adam December 5, 2010, 4:46

    Hi Ronald
    Don’t misunderstand me though as I was making a counter-point with the claim that it is the preferred medium because of its abundance. In reality water is mostly in high-pressure and/or high-temperature phases that don’t support Life-As-We-Know-It. But I also think other biomedia are perfectly possible in our current state of ignorance – some suggested media are super-critical gases, liquid metal carbonyls, ammonia (in various dilutions), hydrocarbons and so forth. Sure, they don’t support Life-As-We-Know-It but to claim that other kinds of life are impossible only gives me a belly-laugh. We really know so very little about what makes Life.

  • Zen Blade December 5, 2010, 10:14

    Eniac,

    A lot of their data were along the lines of “arsenic associates with DNA” or “arsenic associates with lipids”… I associate with all sorts of things, places, people, objects, etc… It doesn’t mean I am one of those places, things, people, objects, but I could be.

    In one figure they show the ratio of P/C vs. As/C in the organism. The figure would be convincing if they had any sort of control, but they don’t. They have two conditions: +As -P and -As +P. This is not +/- 100%, but by making such radical changes without also showing the +As +P and the -As -P, it is difficult to determine if the changes are a result of actual As incorporation, or simply a result of changing growth conditions and the bacteria altering its protein expression profile or altering how it is growing/living. Less P, means less biomolecules that can have P in it. Where does the sacrifice begin? Not with your DNA. However, there will also be selective pressures to reduce the genome…

    Science/Nature papers are infamous for being poorly described/detailed. This paper has a lot of supplemental data, and a wide variety of techniques, but…

    Also, let’s make it clear. Arsenic is a poison. It interferes with normal biochemical pathways. While it seems likely this bacteria is highly evolved (in the sense of resisting As as a poison), that does not mean that the organism is pro-actively replacing P with As. But it could be.

  • Tarmen December 5, 2010, 13:20

    I wonder if we could use this kind of bacteria for something ?? Now that we know about it. Maybe we can bio-engineer some useful species. Perhaps for cleaning up poison soils ? Or in future, for altering poisonous atmospheres of moons and planets ?

  • Athena Andreadis December 5, 2010, 14:47

    The paper did not say that 11% of the phosphorus in the nucleic acids was arsenic, Eniac. It said that 11% of the total arsenic was in the nucleic acids portion. Given how much phosphorus is in proteins versus nucleic acids, this is not much. Nor have they yet done the crucial (and difficult) experiment of finding out who is capable of replicating, giving rise to progeny, rather than accumulating arsenic during the stationary phase.

    I should add that bacteria do all kinds of amazing things routinely, something that biologists know well and are prepared for (relatively obvious example: antibiotic resistance; to those into astrobiology: the exotic alterations of extremophiles). Regarding life’s building blocks, I, for one, have long held the view that the only privileged molecules are carbon and, to a lesser extent, water, because of very specific unique properties.

  • Athena Andreadis December 5, 2010, 14:59

    P. S. to my previous comment: Nor do they distinguish between DNA and RNA. RNA turns over fast and there’s a good deal more of it. If rRNAs and tRNAs (~90% of all RNA) directly incorporate As in their backbone, they can be tolerated because they are expendable. The vital issue is: how much of the DNA backbone has arsenic, if any?

  • Zen Blade December 5, 2010, 20:16

    Athena,

    The problem (I would think) with incorporating As into RNA is that RNA is already inherently more unstable… Having the Arsenate (from what I have heard and read) would make the RNA molecules (which already have a very very short half life) even more unstable. That may be okay, b/c as you said there is a large amount of turnover. And in proks you do have coupled tx/tln. [so less stable mRNA might be okay]

    so, yeah, As may be okay with RNA, but I am not comfortable with that statement.

    I think the organism tolerating As intracellularly is likely the true finding.

  • Athena Andreadis December 5, 2010, 21:39

    Zen, you’re thinking of pre/mRNA — you and I are splicers, so we think almost exclusively of that when we say “RNA”. tRNA and rRNA are stable once they fold. But you have a point. We simply will have to await the results of more refined analysis of the nucleic acids in the As-selected bacteria.

  • Athena Andreadis December 5, 2010, 22:06
  • Eniac December 6, 2010, 0:01

    My thinking is that precisely because arsenic mimics phosphorus so well, it is unlikely that the bacterium is able to keep it out of anywhere, selectively, while letting phosphorus in. That includes DNA. The only way the DNA could remain arsenic free is if it remained unchanged after the arsenic was added. That, however, is incompatible with the observation that the bacteria “grow” under high arsenic conditions, which requires DNA synthesis. One has to assume that as the bacteria grow, any newly synthesized DNA must contain arsenic. Or else, one has to propose a highly selective mechanism that keeps the arsenic out.

  • Athena Andreadis December 6, 2010, 11:22

    Eniac, you’re talking of bacteria as if they are passive bags with pores. In reality they have plenty of, yes, selective ways they can use to exclude arsenic from specific compartments or components. Their evidence that the DNA contains arsenic is looking shakier and shakier, as more people analyze the results.

  • Eniac December 6, 2010, 13:37

    The refutations cited by Athena are very convincing. Ah well, it would have been really neat….

    The question remains how the bacteria keep the arsenic from substituting for phosphorus, but that sure seems like an easier trick than keeping arsenate-DNA from hydrolyzing after 10 minutes. Some tweaking of enzymes in the relevant synthetic pathways for higher phosphate specificity could be all that is needed.

  • bigdan201 December 6, 2010, 13:54

    If nothing else, this arsenic bacteria discovery confirms that life is more resilient and flexible than was previously understood. It is another step in the long-term trend of discovering that life is more plentiful, varied, and hardy than previously supposed, which is an encouraging trend for exobiology.

    After all, if we can find life on earth everywhere from antartic ice, hydrothermal vents, hot springs, nuclear waste, and igneous rocks, it makes it more likely that life has sprung up elsewhere in the universe.

  • andy December 6, 2010, 15:06

    Regarding comments about the abundance of liquid water, it seems fairly plausible that any sufficiently-large, H₂O-rich planet located far enough away from a star will have liquid water at some point during its history. The smaller worlds will cool off faster after their formation and their oceans will freeze, while liquid water in gas giants will be in the form of droplets in the atmosphere. Since smaller planets are more common than large ones, it implies that the majority of the universe’s potential habitats die very young.

  • Tulse December 6, 2010, 15:09

    “if we can find life on earth everywhere from antartic ice, hydrothermal vents, hot springs, nuclear waste, and igneous rocks, it makes it more likely that life has sprung up elsewhere in the universe”

    Not really — there is deep conceptual difference between environments conducive for abiogenesis and environments that existing life could then colonize. Human can live in the Antarctic, under the ocean, even in the vacuum of space, but we could have never evolved originally in those environments. Likewise, organisms can adapt to all sorts of hostile niches that would not support the origination of life.

    My guess is that, whatever life we find, we will learn that its original ancestors arose in warm, wet, chemically and radiologically benign conditions.

  • Jay Lazor December 7, 2010, 0:08

    If the bacterium does incorporate arsenic into its DNA, it suggests that nucleotide polymers can form with both arsenic and phosphorous. This is important because it means abiogenesis can occur under a wider variety of conditions. Felisa Wolfe-Simon suggests that arsenic-RNA may have formed first, and later transitioned to phosphorous. If this was actually the case, we can never know, but she has provided some evidence to support her hypothesis. It’s not compelling evidence, but it is interesting and certainly requires further study.

  • Athena Andreadis December 7, 2010, 10:29

    Jay, arsenic compounds are unstable in water. Their half-life is ten minutes. This bacterium was a regular eubacterium from the E. coli family that did a retroactive adaptation — and the arsenic was provided as arsenate, which means that it required a pre-existing oxygen biochemistry. The evidence that there is arsenic in its DNA is very, very circumstantial and the experiments lack controls and purification steps.

  • Eniac December 7, 2010, 12:10

    Tulse: I agree that the conditions for life and abiogenesis are separate, but I do not think that we have any clue as to how warm or how wet they are/were for abiogenesis, or what “benign” means. For all we know, hard radiation may have been an essential ingredient, warm might have been 400 degrees Cesluius and wet might have been a rtace of water trapped between layers of clay. We don’t know much at all about the temperature and wetness of the origin of our own life, and we will not learn that of any extraterrestrial life we might encounter, either.

  • Eniac December 7, 2010, 12:32

    Athena, I realize cells have selective transporters of all sorts, but normally not ones that work well for Arsenate vs. Phosphate. Otherwise, Arsenic would not be the dreadful poison that it is.

    The huge increase in concentration in the lab over natural levels would overwhelm any membrane transport defenses the critters might have developed while living in Lake Mono. In my view it is more likely that the Arsenic is everywhere in the cell, but is kept out of critical molecular components through enhanced selectivity in the biosynthetic pathways.

  • Athena Andreadis December 7, 2010, 15:56

    Actually, Eniac, for most of the experiments they grew the isolated bacterial colony in As concentrations lower than those in lake Mono. Also, in the discussion threads of one of the critiques I linked to, several people have pointed out that P concentration in most seas is lower than what they admit was in their media. So all you need is an exclusion mechanism, as both you and I have said. Which may explain why these cells have these numerous and enormous vacuoles.

  • Athena Andreadis December 7, 2010, 17:08

    The criticisms are now starting to surface in the popular press. Slate magazine just published a lay summary of the most glaring, obvious problems: http://www.slate.com/id/2276919/