# NASA discovers new lifeform with totally different DNA than anything else

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http://gizmodo.com/5704158/nasa-finds-new-life

This might EASILY be the most amazing discovery in several decades, if not a century.

Seriously, could anyone's theory have anticipated this discovery?

EDIT: Okay it might not be independently evolved from other lifeforms (gizmodo article was too sensationalist). But it's still amazing

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Ygggdrasil
Gold Member
There is reason to doubt that the organisms' DNA really does contain arsenic instead of phosphorus:

[Astrobiologist Steven Benner] was impressed by the finding that bacteria could get by with so little phosphorus and so much arsenic, but he questioned the conclusion that the arsenic was truly taking the place of phosphorus. Benner explained that chemists have long been familiar with the properties of arsenate compounds. "We know, for example, that they fall apart in water quickly," he said. "Those structures are not going to survive in water."

In their paper, Wolfe-Simon and her colleagues say that the GFAJ-1 bacteria can apparently cope with that instability, perhaps because of intracellular mechanisms that keep water out. Benner, however, said that other scientists would have to first confirm that the arsenic is really being taken up the way the paper describes, and then figure out how the process squares with what's already known about biochemistry.

"If this result is true, we've got to go back and rewrite a lot of chemistry," Benner said.

Benner is willing to put his money where his mouth is: "I've wagered Felisa \$100 that that's not arseno-DNA," he told me.
(http://cosmiclog.msnbc.msn.com/_news/2010/12/02/5564852-life-as-we-dont-know-it-on-earth [Broken])

By labeling the arsenic with radioactivity, the researchers were able to conclude that arsenic atoms had taken up position in the microbe’s DNA as well as in other molecules within it. [Biochemist Gerald Joyce], however, said that the experimenters had yet to provide a “smoking gun” that there was arsenic in the backbone of working DNA.

Despite this taste for arsenic, the authors also reported, the GFAJ-1 strain grew considerably better when provided with phosphorus, so in some ways they still prefer a phosphorus diet. Dr. Joyce, from his reading of the paper, concurred, pointing out that there was still some phosphorus in the bacterium even after all its force-feeding with arsenic. He described it as “clinging to every last phosphate molecule, and really living on the edge.”
(https://www.nytimes.com/2010/12/03/science/03arsenic.html)

I'll reserve judgment until I've had time to fully read the study.

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Monique
Staff Emeritus
Gold Member
Actually its DNA normally contains phosphor, the discovery is that it can use arsenic when it doesn't have a source of phosphor. Very remarkable and important discovery, but I would not call it a new life form.

FlexGunship
Gold Member
Actually its DNA normally contains phosphor, the discovery is that it can use arsenic when it doesn't have a source of phosphor. Very remarkable and important discovery, but I would not call it a new life form.
I've been known to use a little arsenic from time to time in my cooking. Wait... no... what's that called? Umm... allspice!

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Actually its DNA normally contains phosphor, the discovery is that it can use arsenic when it doesn't have a source of phosphor. Very remarkable and important discovery, but I would not call it a new life form.
So it has the ability, in an environment lacking phosphorus, to instead use arsenic in the DNA? Can their DNA contain arsenic completely as a 100% substitute for phosphorus?

A comment someone posted on some website:
"Now, if we could make bacteria that utilize germanium (two periods down from carbon) and arsenic, we'd have living semiconductors...think of it...somewhere in the universe Ge/As bacteria may have evolved into a transistor radio that plays "Duke of Earl"."

Is the actual study released yet?

Anticlimactic so far, I have to admit.

Either way, I welcome our new arsenic-loving overlords.
Ahahhaha, love it.

FlexGunship
Gold Member
Ahahhaha, love it.
No more Trekkie-style alien lovefests though. One kiss and you've got a mouthful of arsenic.

Arsenic life always welcomed.

Monique
Staff Emeritus
Gold Member
What I wonder is what the bacterium does instead of phosphorylation, in the absence of phosphor. Arsenicylation?

Monique
Staff Emeritus
Gold Member
The original study: http://www.sciencemag.org/content/early/2010/12/01/science.1197258
Life is mostly composed of the elements carbon, hydrogen, nitrogen, oxygen, sulfur, and phosphorus. Although these six elements make up nucleic acids, proteins, and lipids and thus the bulk of living matter, it is theoretically possible that some other elements in the periodic table could serve the same functions. Here, we describe a bacterium, strain GFAJ-1 of the Halomonadaceae, isolated from Mono Lake, California, which substitutes arsenic for phosphorus to sustain its growth. Our data show evidence for arsenate in macromolecules that normally contain phosphate, most notably nucleic acids and proteins. Exchange of one of the major bioelements may have profound evolutionary and geochemical significance.

bobze
Gold Member
Is the actual study released yet?

Anticlimactic so far, I have to admit.
Yes, its up at sciencemag.org. Just finished reading it and I have to say, I'm not sure why I let myself buy into all the "media hype". As these things normally are, it was over-sensationalized.

The whole reason that arsenic is poisonous is because it is so chemically similar to phosphorous that our enzymes and biochemical pathways can't tell it apart. That an organism evolved the ability to cope with this hurdle under an environment of reduced phosphates and prevalent arsenates is pretty unremarkable considering how clever evolution can be. Certainly no less remarkable that vertebrates that don't use "blood", archaea that thrive in radioactive waste or boiling sulfuric acid or invertebrates that enjoy life at a cozy 176 F and 250+ atms.

Probably the coolest implication from this discovery in my opinion, comes for origins of life research specifically for making nucleotides composed of a nucleoside and arsenate instead of nucleoside and phosphate. The upside to this, is that the reaction (nucleotide formation) happens much more rapid with arsenates and nucleosides (minutes) so could have possibly been the first use of nucleic acid material prior to more complex life.

Are the implications that it uses arsenic in every way the same as it uses phosphorus or only in certain select aplications? Do they use Adenotriarsenate instead of Adenotriphosphate? IMHO if it only uses arsenic where its convienient and easy then its a cute biochemical trick, but if it uses ATAs......thats a real biochemical revolution!!!

bobze
Gold Member
Are the implications that it uses arsenic in every way the same as it uses phosphorus or only in certain select aplications? Do they use Adenotriarsenate instead of Adenotriphosphate? IMHO if it only uses arsenic where its convienient and easy then its a cute biochemical trick, but if it uses ATAs......thats a real biochemical revolution!!!
Right now, they aren't entirely sure. They found that arsenate was present in in the correct ratios that phosphates were to suggest it used them in DNA as well as protein and some lipid.

So yes, they are suggesting that they form nucleoside (adenosine, guanosine, thymidine, cytidine and uridine) mono/di/triarsenates. But we await further confirmation.

As I pointed out earlier, that wouldn't be so surprising because arsenates cause toxicity by your enzymes choosing them and will do this "naturally" because to them arsenate and phosphate is essentially identical. Which is unfortunately why arsenate poisons us lesser beings :)

A comment someone posted on some website:
"Now, if we could make bacteria that utilize germanium (two periods down from carbon) and arsenic, we'd have living semiconductors...think of it...somewhere in the universe Ge/As bacteria may have evolved into a transistor radio that plays "Duke of Earl"."
So, if you submerged bacteria in water (With aqueous germanium or silicon) with no source of carbon at all, would this eventually happen to the bacteria?

What would happen if we ate this bacteria? Would it be like eating arsenic?

Well yes but assumeing you cleansed it off first it would be a extreemly dilute dose, however if you were to dip your hand in the lake im pretty sure it could end badly.

Ygggdrasil
Gold Member
Here is my rather long analysis of the article. I've tried to write it so that non-chemists and non-biologists can understand it. If you're intimidated, you can skip to the last two paragraphs for a summary of my thoughts on the paper.
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Phosphorus is an extremely important element in biology. Found mostly in the form of phosphate (PO43-), phosphorus helps to form and stabilize the lipid membranes that structure the cell, plays important roles in transferring energy throughout the cell, acts as a reversible chemical switch to control many proteins inside the cell, and forms an integral part of the backbone of DNA. With so many diverse an important roles, it would be stunning to find an organism that could survive in the absence of phosphorus. Yet, in research published this week in Science, Felisa Wolfe-Simon and co-workers describe a bacterium that can do just that: live in the absence of phosphorus by using arsenic as a substitute. If true, this work represents a major discovery showing for the first time an organism with a genetic material chemically distinct from the genetic material of all other known terrestrial organisms. However, extraordinary claims require extraordinary evidence. While Wolfe-Simon and co-workers have done an excellent job identifying the arsenophilic bacterium and performing the initial characterization, more work must still be done to rigorously confirm the claims that the bacterium harbors functional arsenic-based biomolecules, in particular arsenic-containing DNA.

Arsenic sits below phosphorus in the periodic table and therefore shares many properties with phosphorus. Because of these similarities, arsenate (AsO43-) could possibly substitute for phosphate in organisms that live in environments rich in arsenate. In order to find such bacteria, the authors took samples from Mono Lake in California, an arsenic-rich lake in California where arsenic-metabolizing bacteria had previously been found. The authors then grew these samples media with no added phosphates and increasing amounts of arsenate over the course of 3 months. At the end of this process, the researchers obtained a bacterial strain, dubbed GFAJ-1, which seemed to incorporate arsenic in the place of phosphorus. This conclusion is based on five lines of evidence:

1) The bacteria exhibit arsenic-dependent growth. The bacteria grow well in the presence of phosphate and absence of arsenate (-As/+P), grow slightly less well in the presence of arsenate and absence of phosphate (+As/-P), and do not grow at all in the absence of both (-As/-P). The fact that the cells grow in +As/-P conditions but not -As/-P conditions suggests that arsenic is required for the cells to grow. It is important to note, however, that the –P samples actually do contain a trace amount of phosphate (3.1µM) compared to 1.5mM phosphate in the +P sample and 40mM arsenate in the +As sample. Because there are trace amounts of phosphate, it is possible that key components of the cell, such as DNA, can still be composed of phosphate. Furthermore, while the data do indicate that the cells require arsenic to grow, they do not pinpoint the exact roles of arsenic. It is completely possible that the bacteria require arsenic for, say lipids and proteins, but still retain phosphorus in their DNA.

2) The bacteria contain high amounts of arsenic and low amounts of phosphorus. The authors measured the amount of arsenic and phosphorus in the cells grown under the –As/+P and +As/-P conditions. Whereas the –As/+P bacteria contain 0.54% phosphorus, the +As/-P bacteria contain 0.02% phosphorus (versus 0.19% arsenic). However, since the authors estimate that ~4% of the phosphorus of the –As/+P bacteria is associated with the genome, the 0.02% phosphorus in the –As/+P bacteria would be sufficient to allow for a normal phosphorus-based DNA.

3) The bacteria incorporate arsenic into biomolecules. By growing the bacteria in a solution of radioactive arsenate, the researchers can track the incorporation of arsenic into biomolecules by following the radioactive signal. The researchers use standard biochemical techniques to perform a crude separation and obtain a fraction containing proteins and small molecular weight metabolites (e.g. ATP), a fraction containing lipids, and a fraction containing nucleic acids (RNA and DNA). They see radioactivity from all of the fractions indicating that arsenic is present in all of these types of biomolecules. The vast majority of the radioactive arsenic signal is present in the protein + small metabolite fraction, but the amount of radioactivity in the nucleic acid fraction is consistent with the amount expected if the DNA contained arsenic. However, it is well known that arsenate can substitute for phosphate; this substitution is the mechanism for arsenate toxicity. In human cells, our phosphate transporters cannot distinguish between arsenate and phosphate and therefore let arsenate into cells. Inside of the cell, some enzymes will substitute arsenate for phosphate, which gums up the cellular machinery eventually killing the cell. Obviously, the arsenate incorporation is not killing these bacteria and some of the arsenate-containing biomolecules are functional, but it is unclear which arsenate-containing molecules are functional and which ones are not, a distinction that cannot be made from the data presented in this paper.

4) Purified DNA from the bacteria contains arsenic. The purified DNA from bacteria grown in the +As/-P condition show more arsenic and much less phosphorus than purified DNA from bacteria grown in the –As/+P condition. However, for the +As/-P bacteria, the DNA still contains much more phosphorus than arsenic (the molar ratio of arsenic to phosphorus is 0.04), although this could be due to a high amount of background phosphate signal from the purification method. Better analyses, including steps to improve the DNA purification, are needed here.

5) X-ray spectroscopy of the arsenic gives signatures consistent with arsenate bound to biomolecules. I’m not very familiar with the technique, so I’ll trust these results at their face value. They give signatures consistent with arsenic incorporation into DNA and proteins, but these signatures are not proof of incorporation into DNA or protein as arsenic incorporation into other metabolites could give similar spectroscopic signatures.

In summary, Wolfe-Simon and colleagues have identified a strain of bacteria that can survive in high arsenic, low phosphorus environments. Surprisingly, this bacteria can use arsenic to replace some of the roles of phosphorus. More work needs to be done to elucidate exactly in which roles arsenic can replace phosphate and in which roles arsenic does not replace phosphate. While the evidence may be consistent with these bacteria containing arsenic-based DNA, the data do not offer irrefutable proof of this hypothesis. A lack of arsenic-based DNA would be expected because previous work by chemists suggests that arsenic-based DNA would be too unstable to exist inside a living cell (Westheimer (1987) Why Nature Chose Phosphates. Science 235: 1173. http://academic.evergreen.edu/curricular/m2o2006/seminar/westheimer.pdf [Broken]).

Nevertheless, Wolfe-Simon have made an important discovery identifying a bacterium where arsenic can replace some of the roles of phosphorus. The organism clearly has novel arsenic-based biochemistries that will be interesting to learn more about in the coming years. While it might be exciting to speculate that these bacteria represent a new form of life with a different type of genetic material than any other terrestrial organisms, we do not yet have enough evidence to say whether this is true or not.

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Thanks for that. The first sentences of the five points make pretty clear to me that arsenic is playing a role in their biochemistry. I wonder though how robust the bacteria are? Does the arsenic provide any clear advantage to their continued evolutionary success even in the most friendly environments to their biochemistry or would they quickly become extinct if their cozy salt lake changed even slightly? Perhaps though the answer is obvious: most (complex) life on (average) earth is phosphate-based and therefore, I would guess, the arsenic, although interesting, is probably not a viable adaptive strategy against sometimes drastically changing environments that phosphate-based organisms have been so successful at overcoming.

Are the implications that it uses arsenic in every way the same as it uses phosphorus or only in certain select aplications? Do they use Adenotriarsenate instead of Adenotriphosphate? IMHO if it only uses arsenic where its convienient and easy then its a cute biochemical trick, but if it uses ATAs......thats a real biochemical revolution!!!
This article says that the native Mono Lake bacteria were cultured in an As rich, phosphorus poor environment. In the cultured bacteria As does replace phosphorus (P) in ATP yielding ATAs. I don't know if this is the case in the native strains, but if it isn't, then it detracts from the significance of this discovery. In any case, it's still not all that remarkable. Now silicon replacing carbon, that would be something!

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Borek
Mentor
Perhaps though the answer is obvious: most (complex) life on (average) earth is phosphate-based and therefore, I would guess, the arsenic, although interesting, is probably not a viable adaptive strategy against sometimes drastically changing environments that phosphate-based organisms have been so successful at overcoming.
Note that abundance of P on Earth is about 1000 higher than As. In most environments there is plenty of P available (as compared to As).

http://en.wikipedia.org/wiki/Abundances_of_the_elements_(data_page [Broken])

Also note numbers listed are mass fractions, we should be looking at molar fractions, that would mean even twice less As.

So even if they were interchangeable, P would be preferred just because of its availability.

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Ok, then what about just bond energies. Take just ATP and ATA. What is the energy difference in cleaving a phosphate off of ATP and a what $AO_4$ off of ATA? What about the phosphate-ribose bond in nucleic acids? What is the energy difference in the analogous $AO_4$-ribose bond? Would be interesting to know if it's less or more than for phosphate. If it's less, then these molecules are less stable. If it's more, then the energy required would perhaps cause other species in the surrounding medium to be susceptible to this energy abundance causing them to be less stable. I assume in this particular bacteria, these energy adjustments and associated (chemical) species have adapted through Natural Selection. Just how much adaptation is needed to account for this energy difference?