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This image shows a type of bacteria called GFAJ-1 that was said to incorporate arsenic in its cellular machinery.
Researchers say they ran a more rigorous version of the experiment that sparked a yearlong debate over the prospects for arsenic-based bacteria — but found no trace of arsenic within the organisms' DNA.
The findings, submitted to the journal Science this week and distributed openly via the ArxiV.org website, serve as the most definitive refutation to date of the "weird life" claims that caused such a stir in December 2010. "They match with what basically all the scientists had concluded a year ago," University of British Columbia microbiologist Rosie Redfield, the paper's senior author, told me.
Redfield had criticized the original study from the start, suggesting that the arsenic detected in a strain of bacteria known as GFAJ-1 was not actually incorporated into the machinery of life but was merely the result of insufficient purification. "We were much more meticulous about purifying the DNA before we analyzed it," she said today.
She and her colleagues worked with the same bacteria used for the original research, which had astrobiologist Felisa Wolfe-Simon as lead author and was published in Science. The bacteria were bred to live in a high-arsenic environment, with virtually no phosphorus present. The aim was to see whether arsenic compounds known as arsenates, which are typically poisonous to life as we know it, could be substituted for chemically similar phosphorus compounds known as phosphates. If that turned out to be the case, that would suggest that alien life forms could operate using biochemical processes radically different from Earth's.
In their paper, Wolfe-Simon and her colleagues said they saw evidence that the bacteria could be bred to live in the arsenic-rich environment, and that arsenates were detected in "macromolecules that normally contain phosphate, most notably nucleic acids and proteins."
Redfield and her colleagues were able to grow the bacteria amid high arsenic levels, under special conditions, but they found that the arsenic wasn't necessary for the bacteria's survival — and that the highly purified DNA from the bacteria did not contain detectable levels of arsenate.
Redfield noted that some arsenate stuck to the DNA even after what she thought would be sufficient purification, but was removed during a second round of washing. "That shows that arsenate does persist through steps in the DNA purification, but in a form that will wash away," she told me.
The researchers acknowledged that arsenate might occasionally get into the bacteria's biological machinery.
"Given the chemical similarity of arsenate to phosphate, it is likely that GFAJ-1 may sometimes assimilate arsenate into some small molecules in place of phosphate, such as sugar phosphates or nucleotides. Our results do not rule out the possibility that such assimilation could be beneficial," they wrote. "When it comes to DNA synthesis, however, GFAJ-1 does not appear to productively assimilate any arsenate."
Open review for results
The scientists behind the original study have said they would refrain from commenting on follow-up research until the peer-review and publication process is completed. Wolfe-Simon did not immediately respond to an emailed request for comment, but Science News' Rachel Ehrenberg quoted her as saying she and her colleagues never actually claimed that arsenate was being incorporated in GFAJ-1’s DNA.
"As far as we know, all the data in our paper still stand,” Science News quoted Wolfe-Simon as saying in an email. “Yet, it may take some time to accurately establish where the [arsenic] ends up."
That response left Redfield figuratively scratching her head — and literally wondering "WTF??" in a Twitter update. She pointed to several references in the original Science paper referring to DNA, including a sentence saying that the measurements "specifically demonstrated that purified DNA extracted from +As/-P [high-arsenic, low-phosphorus] cells contained As [arsenic]."
The paper written by Redfield and her colleagues is open for review and comment even in advance of its consideration for journal publication. That's consistent with Redfield's advocacy of an "open science" approach to research, as reflected in the regular updates posted to her RRResearch blog. Thanks to the blog, avid followers of the #ArsenicLife issue have known for weeks that the original results couldn't be replicated.
Redfield said she has received assurances that freely distributing the draft paper won't hurt the prospects for publication in Science — which goes against the traditional grain for peer-reviewed publication.
"What's happening, and I'm really pleased by this, is that interested people are reading the manuscript, and they're putting comments on it," she observed.
Redfield said she and her colleagues appreciated the feedback being posted to her blog by experts — as well as by non-experts. "Their comments are going to let us polish the manuscript to make it more accessible to non-experts," she told me.
More about the arsenic-life debate:
- A year later, the debate still percolates
- Nature: Study challenges existence of arsenic-based life
- Chemical & Engineering News: The arsenic aftermath
In addition to Redfield, the authors of "Absence of Arsenate in DNA From Arsenate-Grown GFAJ-1 Cells" include M.L. Reaves, S. Sinha, J.D. Rabinowitz and L. Kruglyak.
Alan Boyle is msnbc.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter or adding Cosmic Log's Google+ page to your circle. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for other worlds.
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Although it is a shame, from a philosophical perspective, to discover that the original findings about arsenic-based life were inaccurate, I am glad that further study on the behalf of Mrs. Redfield and her colleagues prevented the perpetuation of false belief.
That's called science.
Good followup. That IS how science works.
What a shame. A lifeform completely separate from every known species would've been quite the boon. Not only would it open the floodgate for all kinds of research, it would support the possibilities for extraterrestrial life by proving that life can come to be in more than just one way.
I'm sure there was an article I remember reading for microbes that were found living in a methane lake on Earth(Should try to google it). It's also an arguement that their may be methane based lifeforms on Saturn's moon, Titan.
Methane exists in liquid form at -82 C. There are no "methane lakes" on Earth.
It was a hydrocarbon lake not a methane lake.
"Various scientists have suggested that it is the closest thing on Earth to the kind of hydrocarbon lakes that we can see on Saturn's moon Titan. Naturally, these scientists would very much like to answer the question of what kind of life these places can support."
http://www.technologyreview.com/blog/arxiv/25051/
Thank you both for your correction.
honestly I thought they was the case from the start... I just though though it was just more immune to the damage arsenic could do not necessarily having it as part of its path to survival with incorporation of arsenic into the DNA.
As long as no germs were harmed during the making of this experiment...
HaHaHa!!! One of the fundamental beliefs of the evolutionists is proved inaccurate. What will the "primordial soup" lichen's turn to now?
Can someone tell me if barny's post made any sense?
no doug... it did not. I thought only evil cartoon characters started statements with "HaHaHa!!!"
Yeah, this really had nothing to do with evolution and more on extraterrestrial life.
score for scientific process - and by the way scientists too can lie/obfuscate/fudge/fib/etc.
Sure, but nature always exposes them eventually. You can fool some of the people all of the time, and all of the people some of the time, but you can't fool the whole universe, ever.
It's good for people to see the process happening in the clear light of day. It's good that there have been no grandiose claims by the researchers. The media on the other hand......
The original press conference that NASA presented might have been a bit much given how preliminary everything was. I suspect that the early result intrigued them and they were pleased to have some one as charming and telegenic as Dr. Wolfe-Simon out in front.
A good day for Science. A good day for Open Science where research is open for free for public access and comment, which is far better for Science and Society than the current wealthy-only access.
A very very bad day for Wolfe-Simon and for NASA who hailed the original claims with little regard for the Scientific Process.
I am no scientist, but could someone educate me on the following. Since the follow up experiment has not been fully scrutinized, could it be also possible that the arsenates were actuall part of the DNA an were actually removed by the purification process?
Also, the article provided the following: "...it is likely that GFAJ-1 may sometimes assimilate arsenate into some small molecules in place of phosphate, such as sugar phosphates or nucleoitdes. Our results do not rule out the possibility that such assimilation..."
Doesn't that quote indicates that there is still a possibility arsenates could actually be integrated by the bacteria into their system and survive making it a unique and completely type of life form?
Thanks in advance for your responses.
This is one reason why science today has lost the respect of the general public. The horrible manner in which Wolfe-Simon was attacked on this was reminiscent of the Spanish Inquisition. There was no civil-mannered disagreement between researchers. This was a witch hunt for the purpose of producing a heretic to be publicly burned at the stake.
Many people no longer trust those who label themselves scientists or experts because the expertise and science is more like politics and religion than learned individuals seeking ways to extend human knowledge.
Physically speaking, when purifying DNA it is precipitated to the bottom of a tube and then the pellet is rinsed several times with different solutions to clean it. Molecules like RNA, sugars, and salts will also precipitate and that's what the rinsing is suppose to get rid of. The technical question being asked here is: did the first team throughly clean the DNA sufficiently? If not, lots of things, even just free arsenic salts in solution could have been contaminating their "pure" DNA sample leading to the wrong conclusion.
With specific respect to your question, the second team does not rule out the possibility that in such a high arsenic environment is may have been occasionally incorporated, in the place of phosphorus, into small molecules that would have precipitated with the DNA, i.e. sugar phosphates and nucleotides, the building blocks of DNA/RNA. Finding arsenic in these molecules in small amounts would not be surprising, because the phosphates and arsenates are free to exchange in solution and a high concentration of arsenate only increases this chance.
Overall, the reason why this first study was so ridiculed was that the authors fundamentally ignored the fact that the bonds arsenate makes with carbon are fundamentally unstable in water (kind of important for all life). A cell might not be able to control free exchange from occurring in water, but it has a pretty huge incentive to not mis-incorporate a spontaneously dissembling molecule into its one DNA blue-print.
This bacteria should not be ignored however. Arsenic is poison in the cell for many, many reasons mostly boiling down to the fact that a poisoned cell starts spending too much or its energy sorting out arsenic containing molecules or repairing the damage that occurs when a mistake does occur. These bacteria have fundamentally overcome the problem of arsenic poisoning which effects all carbon-based life forms.
This was brief, but I hope this helps. Now I have to go back to my bench and precipitate some DNA of my own. :)
Thanks Biochemist!