Published online 2 December 2010 | Nature | doi:10.1038/news.2010.645
Updated online: 9 December 2010

News

Arsenic-eating microbe may redefine chemistry of life

Oddball bacterium can survive without one of biology's essential building blocks.

Mono Lake tufa towersA bacterium in California's arsenic-filled Mono Lake performs a novel chemical trade-off.Feargus Cooney/Lonely Planet Images

A bacterium found in the arsenic-filled waters of a Californian lake is poised to overturn scientists' understanding of the biochemistry of living organisms. The microbe seems to be able to replace phosphorus with arsenic in some of its basic cellular processes — suggesting the possibility of a biochemistry very different from the one we know, which could be used by organisms in past or present extreme environments on Earth, or even on other planets.

Scientists have long thought that all living things need phosphorus to function, along with other elements such as hydrogen, oxygen, carbon, nitrogen and sulphur. The phosphate ion, PO43-, plays several essential roles in cells: it maintains the structure of DNA and RNA, combines with lipids to make cell membranes and transports energy within the cell through the molecule adenosine triphosphate (ATP).

But Felisa Wolfe-Simon, a geomicrobiologist and NASA Astrobiology Research Fellow based at the US Geological Survey in Menlo Park, California, and her colleagues report online today in Science1 that a member of the Halomonadaceae family of proteobacteria can use arsenic in place of phosphorus. The finding implies that "you can potentially cross phosphorus off the list of elements required for life", says David Valentine, a geomicrobiologist at the University of California, Santa Barbara.

Many science-fiction writers have proposed life-forms that use alternate elemental building blocks, often silicon instead of carbon, but this marks the first known case in a real organism. 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.

Element of surprise

Wolfe-Simon thought the parallels between the two elements could mean that despite its toxicity, arsenic was capable of performing phosphorus's job in the cell. Her search for an organism that would not just tolerate arsenic but make biological use of it took her to Mono Lake in eastern California. The 180-square-kilometre lake has an extremely high arsenic concentration, owing to arsenic-bearing minerals that wash down from nearby mountains.

Wolfe-Simon and her colleagues collected mud from the lake and added the samples to an artificial salt medium lacking phosphate but high in arsenate. They then performed a series of dilutions intended to wash out any phosphate remaining in the solution and replace it with arsenate. They found that one type of microbe in the mix seemed to grow faster than others.

The researchers isolated the organism and found that when cultured in arsenate solution it grew 60% as fast as it did in phosphate solution — not as well, but still robustly. The culture did not grow at all when deprived of both arsenate and phosphate.

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.

The team used two different mass-spectrometry techniques to confirm that the bacterium's DNA contained arsenic, implying — although not directly proving —that the element had taken on phosphate's role in holding together the DNA backbone. Analysis with laser-like X-rays from a synchrotron particle accelerator indicated that this arsenic took the form of arsenate, and made bonds with carbon and oxygen in much the same way as phosphate.

"Our data are strongly suggestive of arsenic replacing phosphorus," says Wolfe-Simon, adding that if the relatively common Halomonadaceae microbe can do it, others probably can too. "It may be an indication of this whole other world nobody has seen," she says.

A world of possibilities

Mary Voytek, who heads NASA's astrobiology programme in Washington DC, agrees that the results are persuasive. "I think no single one of their measurements can prove" that arsenate is doing what phosphate normally would, she says, but taken together, "I will conservatively say that it's very hard to come up with an alternative explanation."

To be truly convincing, however, the researchers must show the presence of arsenic not just in the microbial cells, but in specific biomolecules within them, says Barry Rosen, a biochemist at Florida International University, Miami. "It would be good if they could demonstrate that the arsenic in the DNA is actually in the backbone," he said.

Also, he says, the picture is still missing an understanding of what exactly the arsenic–phosphorus switch means for a cell, says Rosen. "What we really need to know is which molecules in the cell have arsenic in them, and whether these molecules are active and functional," he says.

For example, if phosphate in ATP was exchanged for arsenate, would the energy-transfer reaction that powers a cell be as efficient? In metabolic processes in which arsenate would bind with glucose, would the bonds it forms — weaker than those of phosphate — be as effective? And phosphate groups bind to proteins modify their function, but would arsenate work as well?

"As a chemist, I'm obsessed with details," says Rosen. "I think future studies will really have to tie down how this organism does it."

Others held deeper reservations. "It remains to be established that this bacterium uses arsenate as a replacement for phosphate in its DNA or in any other biomolecule found in 'standard' terran biology," says Steven Benner, who studies origin-of-life chemistry at the Foundation for Applied Molecular Evolution in Gainesville, Florida.

Arsenate forms much weaker bonds in water than phosphate, that break apart on the order of minutes, he says, and though there might be other molecules stabilizing these bonds, the researchers would need to explain this discrepancy for the hypothesis to stand. Still, the discovery is "just phenomenal" if it holds up after further chemical analysis, Benner adds. "It means that many, many things are wrong in terms of how we view molecules in the biological system."

ADVERTISEMENT

In addition to questioning the long-held assumption that phosphate is absolutely required for life, the existence of the bacterium "provides an opportunity to really pick apart the function of phosphorus in different biological systems", notes Valentine. There may even be a way to use the arsenic-loving microbes to combat arsenic contamination in the environment, he adds.

Meanwhile, Wolfe-Simon and her colleagues agree that there is a lot more to be done. The first step is to see whether these or other bacteria replace phosphate with arsenic naturally, without being forced to do so in the lab, she says. The group also has plans to sequence the microbe's genome.

"We have 30 years of work ahead to figure out what's going on," says Wolfe-Simon. 

Updated:

In the light of various criticisms of the findings, Nature has posted a "follow-up":http://go.nature.com/4EQ18o story.

Comments

If you find something abusive or inappropriate or which does not otherwise comply with our Terms or Community Guidelines, please select the relevant 'Report this comment' link.

Comments on this thread are vetted after posting.

  • #16409

    Chemical & Engineering News 88(48) 4 (2010), 29 November 2010, Letters to the Editor, "Hungary's Red Mud"

    http://www.mazepath.com/uncleal/c_en01a.png
    center of page. Arsenic biochemistry is common – but not on land.

  • #16414

    This is definitely a very interesting and important research, but I could live without the media hype.

    It is inaccurate to say that "you can potentially cross phosphorus off the list of elements required for life". The necessary conditions would at best replaced to "carbon and oxygen and ... and (phosphorous or asrenic)". It is very different from really scratching both out the list.

    I am excited with the news, but I only think we can be excited with what it is really all about. Down with the hype!

  • #16415

    Uncle Al Schwartz: Yes, there are plenty of organisms that use arsenic in redox reactions. But this case is fundamentally different – we're not just talking about electron transport here, this bug actually incorporates As into the DNA backbone itself, where you would expect to find phosphorus!

    I'm not sure you can even call that DNA any more. AsDNA?

  • #16417

    I don't understand why people like Nicolau Werneck want to keep science and interesting information to themselves and relegated to the science community. If the general public gets interested in something scientific, that's a great thing! Yes, the writers that write for the general public need to do a better job at explaining things, but that's the editor's fault if they don't.

    A scientific appreciation of life should be available for everyone, not just people with Science Online accounts.

  • #16418

    Really amazing!

  • #16419

    Can we classify this bacteria as organic organism or will the definition of the organic be extended to add Arsenic to the the current six elements namely hydrogen,carbon,oxygen,nitrogen and phosphorous?
    But it is very interesting discovery and it open the possibility that somewhere in the universe there may be life forms thriving based on a totally different model.
    We are one step closer to answering the question "Are we alone in the universe?"

  • #16421

    A really great piece of research, I hope it holds up to confirmation. As Jeff Goldblum said in Jurasic Park said, life finds a way.

  • #16423

    It is amazing.
    Think about its evolution, how it is evolved and what it will evolved to be?
    Can you get the answer? Is there any offspring of this creature?

  • #16426

    Aside from the scientific significance of this discovery, which I'm not qualified to weigh in on, I'm really glad that Mono Lake is even there now for this discovery to be made. There was a long, hard battle to save it from excessive tributary diversions to slake the thirst of Los Angeles. I'm glad I was able to put my money where my mouth was for part of that time. Farther back in time, the more southerly Owens Lake was deprived of all its water supply for Los Angeles, and is mostly a toxic playa now. The film "Chinatown" told part of that story. This is a good example of how vigorous conservation efforts can result in a valuable serendipitous scientific discovery. This can happen anywhere – not just in tropical rain forests for new medicines.

  • #16435

    A possible explanation here:

    http://golden-ratio-in-dna.blogspot.com/2010/12/why-arsenic-could-replace-phosphorus.html

  • #16441

    a beginning of theoretical explanation in:

    http://golden-ratio-in-dna.blogspot.com/2010/12/why-arsenic-could-replace-phosphorus.html

  • #16456

    If As can be used in place of P then we have to imagine that N could do the same under other conditions such as very low temperatures.

  • #16459

    The biggest thing that jumped out at me today, reading about the arsenic surviving proteobacteria, is that someone specifically set out to find them. These creatures are interesting because they replace phosphate with arsenate in all of their cellular processes. (Phosphate is integral in all other life, as it makes up ATP (energy) and is a vital building block of DNA.) More interesting, the sleuthing of where to look for something like this came from a NASA geochemist who was looking for them. A silicon based life form has become a tripe in modern scifi worlds. It is easy fun science: sitting directly below carbon is the heavier but similarly reactive silicon is just waiting to complete/seemingly-defy the second law of thermodynamics as carbon has. Why hasn’t anyone real look for silicon based (non-diatom) life on EARTH?
    Where are the silicon rich areas of the world, where it interfaces with water and heat? Pretty much everywhere, as quartz is made of silcon and it is one of the Earth’s crust’s favorite rocks. But there are spots where the collection would be grander? right?
    I would look in two places: The middle of the sandy areas of Africa. Where silica dust congregates because of the winds. In some of the less temperate environments, a silica dust rich desert could be remote enough to spawn if not silicon based life, but silicon-exchanging life. Near water in such an environment, the evolution possibly exists that a bacteria or algae could opt to intermittently switch from using carbon in some cellular processes in deference for a silicon. No-one has looked for that either.
    The Atlantic is feed silica on the winds, which feeds a plankton population the chemicals to build their “glass” encasements. In each hemispere of the Atlantic exists spinning gyres that circulate the air and ocean current in predictable paths that have existed for millions of years. It would stand to reason that the gyres could act as a funnel of silicon in two spots of the Atlantic Ocean. Fed by the west blowing winds of Africa’s internal deserts, these gyres would, to some degree, offer a higher silicon count lending to the possibilities of ecosystems using silcon as a carbon stand-by. Find me funding for a NOAA style oceanographic ship, and I’ll find you one place that either does have silicon based life or ...not...

  • #16460

    The biggest thing that jumped out at me today, reading about the arsenic surviving proteobacteria, is that someone specifically set out to find them. These creatures are interesting because they replace phosphate with arsenate in all of their cellular processes. (Phosphate is integral in all other life, as it makes up ATP (energy) and is a vital building block of DNA.) More interesting, the sleuthing of where to look for something like this came from a NASA geochemist who was looking for them. A silicon based life form has become a tripe in modern scifi worlds. It is easy fun science: sitting directly below carbon is the heavier but similarly reactive silicon is just waiting to complete/seemingly-defy the second law of thermodynamics as carbon has. Why hasn’t anyone real look for silicon based (non-diatom) life on EARTH?
    Where are the silicon rich areas of the world, where it interfaces with water and heat? Pretty much everywhere, as quartz is made of silcon and it is one of the Earth’s crust’s favorite rocks. But there are spots where the collection would be grander? right?
    I would look in two places: The middle of the sandy areas of Africa. Where silica dust congregates because of the winds. In some of the less temperate environments, a silica dust rich desert could be remote enough to spawn if not silicon based life, but silicon-exchanging life. Near water in such an environment, the evolution possibly exists that a bacteria or algae could opt to intermittently switch from using carbon in some cellular processes in deference for a silicon. No-one has looked for that either.
    The Atlantic is feed silica on the winds, which feeds a plankton population the chemicals to build their “glass” encasements. In each hemispere of the Atlantic exists spinning gyres that circulate the air and ocean current in predictable paths that have existed for millions of years. It would stand to reason that the gyres could act as a funnel of silicon in two spots of the Atlantic Ocean. Fed by the west blowing winds of Africa’s internal deserts, these gyres would, to some degree, offer a higher silicon count lending to the possibilities of ecosystems using silcon as a carbon stand-by. Find me funding for a NOAA style oceanographic ship, and I’ll find you one place that either does have silicon based life or ...not...

  • #16462

    Hello MFAJ-1, Here is the original structure of a bacteria a live adaptation process of the building to nature

  • #16469

    Although well known, the possibility of silicon based life isn't taken very seriously by most astrobiologists. Carbon is happy with angled bonds, as in benzene, but silicon prefers linear bonds. As a result carbon based compounds have a lot of structural diversity but silicon produces linear molecules with little structural diversity. It may, from memory, have been Sagan who first pointed this out. The chemistry of elements in the same column is similar but not identical.

  • #16473

    I was captivated,beyond my learning rim-GCSE pupil, by the content of this article. I am thrilled by this revelation of the new ideas of life, so much so, that I have started to think about my chance to study this subject.

  • #16482

    If reviewers and journalists would have read the paper carefully, they would have noticed that there is no real proof of substition of P by As. It only proved that As have been accumulated on DNA.

    If reviewers had some understanding of chemistry they would also have rejected this affirmation of substitution of P by As. It is impossible to have covalent As links within water (see other comments from John Sutherland from the MRC Laboratory of Molecular Biology ,.....)

  • #16488

    revolutionary object.

  • #16491

    Claims made in the paper and even more comments in other media are in my opinion greatly exaggerated.

    Certainly the described bacteria do not represent a new form of life, as claimed.
    What the article actually describes is the adaptation of bacteria to high levels of arsenate, without explaining the molecular mechanism of this adaptation.

    The species of bacteria described in this paper have many close relatives. If it were radically different from other life forms its genetic code would have been vastly different. This suggests that a minor change, with specialization for environment with high levels of arsenic. Authors were able to determine the 16S RNA sequence of these bacteria. If bacterial genome would contain arsenic instead of phosphorus is very likely that the enzymes used for sequencing would be unable to perform the same reactions as for the normal DNA, yet no problems of this kind are mentioned.

    The article is full of holes and reviewers should have asked for some simple additional experiments to support such strong claims. Replacement of phosphorus by arsene could have been very easily demonstrated by determination of the molecular weight of components (nucleotides from DNA hydrolysate) or lipids – mass spectra should very clearly identify if they contain arsenic or phosphorus.

    The most important argument in the article is that arsenic replaces phosphorus in biological macromolecules. The analysis shows that bacteria still contain phosphorus, which apparently originated from the reagents (probably arsenate) which was added to the medium. The article does not indicate in the materials section what was the source and purity of arsenate used for media preparation, particularly with respect to the content of phosphates in it. Given that bacteria do not grow without either phosphate or arsenate may suggest that the arsenate could provide sufficient phosphorus contaminants to sustain bacterial growth (which is anyway slower than with the addition of phosphorus). The As:C ratio of DNA reduces to much lower ratios than analysis of whole cells, which may be full or (presumably) arsenic containing vacuoles. And so on...

    My interpretation is that the described bacteria may contain the system for salvaging phosphate from the large background concentration of arsenate. Arsenate is probably deposited into vacuoles (probably in the form of complexes with organic compounds), while the phosphate is used for the construction of normal biological building blocks.

    This is certainly an interesting finding but far from the life without phosphorus.

  • #16496

    Roman, I don't have access to the online paper so I haven't read it yet but over on New Scientist's discussion someone claims that the growth medium has 3 micomolar phosphorus.

  • #16508

    An excellent review here: http://rrresearch.blogspot.com/2010/12/arsenic-associated-bacteria-nasas.html?spref=fb

  • #16517

    Life is really full of mysteries. A large finding about extraterrestrial existence could be announced Thursday at a National Aeronautics and Space Administration press conference. National Aeronautics and Space Administration appears to be following Apple's model of press relations. A mystical event has been declared and the Internet has erupted with predictions about its nature. The documented work of researchers presenting their findings at the press conference lead some to conclude that proof of existence on other worlds has become confirmed.

  • #16529

    This is a fantastic discovery but the concern is how widespread this would be in nature. Under the competition ,phosphorus had more advantage compared to arsenic as evidenced by predominance of phosphorus in the biological system.

    Rajesh Mehrotra,BITS ,Pilani,India.

  • #16540

    This is the exciting side of science and research. If all "facts" are already established... where will we find satisfaction? we have to deeply look in other people beliefs and cultures, some are convincied that we knew nothing yet!

    scientifically, I am excited how the tetrahedral, with As intead of P, is thermodynamiically maintened which deltaH, which entropy?

  • #16549

    If As really is in the backbone of DNA, I wonder will this revert to P in a "P rich, As poor or deficient" medium after some time. Is this possible as a result of some kind of degeneracy for P or As specificity in the responsible synthetic and metabolic enzymes or what? I'm really curious...

  • #16550

    If As really is in the backbone of DNA, I wonder will this revert to P in a "P rich, As poor or deficient" medium after some time. Is this possible as a result of some kind of degeneracy for P or As specificity in the responsible synthetic and metabolic enzymes or what? I'm really curious...

  • #16552

    It's is innovative work to help all those people who are highly affected with "Arsenic poisoning" in developing country like Bangladesh, West Bangal of India. Recently I heard similar news on CNN-IBN that Dr.S Shivaji are also working on Biodiversity of Arsenic eating bacteria from India. I hope this will bring good hope in near future.

  • #16553

    It's is innovative work to help all those people who are highly affected with "Arsenic poisoning" in developing country like Bangladesh, West Bangal of India. Recently I heard similar news on CNN-IBN that Dr.S Shivaji are also working on Biodiversity of Arsenic eating bacteria from India. I hope this will bring good hope in near future.

  • #16615

    An update to this story has been posted here, focusing on the controversy over the paper.
    Thank
    Ananyo (Online editor)

  • #16659

    This is more of a story about phosphorus than arsenic. Obviously, the communities' knowledge of phosphorus is incomplete and speculation about arsenic-based life gains no scientific ground... this is fodder for a science fiction movie at this point, albeit, it is holding my interest. It is fairly common knowledge that trace minerals are essential to healthy human life; we might find, if it isn't already found, that arsenic is vital to us, or at least since it holds some similarities to phosphorus, might be used by the body in its' place.

  • #16715

    Unbelievable!

  • #16762

    Molybdate, Chromate, Arsenate are known as oxidizing agents and their toxic effects to SRB Bacteria are well known.
    Molybdate ions are toxic to SRB bacteria only above certain critical concentrations. Below the critical concentrations Molybdate ions activate the effect of SRB bacteria. Molybdate ions react with phosphate ions to produce non toxic Phospo-Molybdate ions only at certain ratio of Molybdate /phosphate ions. Similarly arsenate ions can react with phosphate ions especially at high arsenate/phosphate ratio to produce a compound which is non toxic to SRB bacteria. This reaction is very well known and established as a method for the determination of phosphate ions using excess of Molybdate ions. It is possible that Arsenate ions react with phosphate to produce a non toxic Phospo-Arsenate.

    M. Reda
    CanadElectrochim
    Calgary Alberta Canada

  • #17257

    this has definitely opened new doors in terms of how we looked towards evolution and the role of elements, but the authors have yet to prove that As is present in the DNA backbone

  • #23633

    Though many speculations have been made about the finding, yet if, it gets conformed..then it may lead to new insights how life originated & evolute on EARTH, & even how it may further evolve in the course of time..

    S. Debnath
    IMTH
    SBT,KIIT University
    Bhubaneswar
    INDIA

  • #26830

    The last bit about whether or not the process happens organically rather than being "forced to in a lab" is quite interesting. It's like live blood cell analysis. When blood is tested after it's been dried for several days, the test isn't a true indication of what's going on <a href="http://www.gainmuscleandloseweight.com/vince-delmonte-review/">inside the body</a>. Same in this case, it must be tested outside the lab.

    The very end where the scientist admits there's at least "30 years of work" to be done is telling. Honestly I don't think we really understand any more than about 1% of true organic chemistry of life. They've found mushroom spores in space for crying out loud. To what degree does the macro universe correlate to subatomic particles? There's so much to learn. I just wish I could live another thousand years to see it all.

  • #28341

    i think i remember a movie entitled "Evolution". It was a hilarious movie. I remember them mentioning that arsenic is considered a poison to us carbon based life forms then they went on to discover the weakness of their enemy based on the basic element of that life form (i forgot what it was), then by following the same pattern on the chemical table, they discovered selenium to be its weakness. anyway, just sharing a funny story. The title just reminded me of it.

    <a rel="dofollow" href="http://www.gettingmyexbacktips.com/pdf-ebook-reviews/pull-your-ex-back-review/">buy pull your ex back</a>

  • #28719

    Honestly I don't think we really understand any more than about 1% of true organic chemistry of life.
    Buy Essay
    Buy coursework
    Buy Assignment
    Buy Dissertation
    Buy Thesis

  • #29563

    Venlor is a medicine available in a number of countries worldwide. venlor Clonidine belongs to a class of drugs called central alpha-adrenergic agonists. buying clonidine Prednisone safety decreases the chance for undesirable side effects. buying prednisone Protonix belongs to a group of drugs known as proton pump inhibitors. buying protonix Buy forzest to improve your performance in bed. buy forzest Cipro is a drug used to treat infections of the skin, lungs, airways, bones etc. buying cipro

  • #29568

    Tadacip manufactured by Cipla is a medication used for treating male impotence. tadacip 20 Revatio is used to treat pulmonary arterial hypertension. buy revatio Nizagara is a treatment option for erectile dysfunction. nizagara

    Buy nizagara online. buy nizagara nizagara tablets Liponexol is an exclusive development of the scientific support of the plant components. liponexol

  • #29569

    Prednisolone is a drug that is an active metabolite of prednisone that is used in treating conditions similar to those listed here. buying prednisolone Tadacip is developed and manufactured by an Indian pharmaceutical company Cipla. tadacip 20 mg Revatio online for the treatment of pulmonary arterial hypertension appears to improve exercise capacity. revatio online

    Valtrex used to treat infections caused by herpes viruses. buying valtrex Zebeta is a beta-blocker and is used to treat high blood pressure. buy zebeta Acomplia is the most effective and fast weight loss diet pills available in UK. buying acomplia

  • #32307

    melanin is what gives the body color, right? well, the more you have the darker one is, however, african americans are at increased risk of vitamin d deficiency related to insufficient penetration of sunlight to the skin. calcul imc

  • #33387

    gradually we perceive as our knowledge of our own race are limited

    vivo gestao empresas

  • #36769

    Thanks for the great article Alla, keep up the good work
    Web Design Design Jobs

  • #38334

    I love stories like this. It makes it more of a well-known fact that we're NOT alone in this universe. There is a higher power out there and we haven't figured everything out yet. Scientists still having jobs should be proof enough of that.

    How did they figure that out anyway? Were some scientists out there duck hunting or something?

    This is for those who don't know what <a href="http://www.duckhunting.com">Duck Hunting</a> is! :P

  • #38335

    I love stories like this. It makes it more of a well-known fact that we're NOT alone in this universe. There is a higher power out there and we haven't figured everything out yet. Scientists still having jobs should be proof enough of that.

    How did they figure that out anyway? Were some scientists out there duck hunting or something?

    This is for those who don't know what Duck Hunting is! :P

Add your own comment

This is a public forum. Please keep to our Community Guidelines. You can be controversial, but please don't get personal or offensive and do keep it brief. Remember our threads are for feedback and discussion - not for publishing papers, press releases or advertisements.

You need to be registered with Nature to leave a comment. Please log in or register as a new user. You will be re-directed back to this page.