NASA’s ‘ET’ suffered arsenic poisoning!
Published: 7 December 2010 (GMT+10)
NASA published a short and cryptic press release on 29 November: they commented that they were arranging a news conference for 2 December “to discuss an astrobiology finding that will impact the search for evidence of extraterrestrial life.”1 The obviously intended effect occurred pretty much immediately: the media and internet were set buzzing with widespread speculation as to what exactly this could mean, ranging from the prosaic to the preposterous.
It turns out it was much more prosaic than even many more circumspect commentators had speculated: they discovered evidence that a bacterial strain found on Earth was capable of metabolizing arsenic (As) and incorporating it into structural molecules of the cell.2 Researchers found a strain of gamma proteobacteria known as GFAJ-1, found at Mono Lake in California, can feed on As and incorporate it into its biological structures when there was a shortage of phosphorus (P).3
Knowledge that As is positively utilized in biology has only come to light in the last 15 years. Arsenic has been shown to be an important part in both respiration and photosynthesis for a wide variety of bacteria,4 including gammaproteobacteria.5 However, this latest finding is qualitatively different because rather than merely using As in its inorganic forms (arsenite (AsO3–) and arsenate (AsO43–)) to provide energy, GFAJ-1 incorporates arsenate into biochemical structures normally occupied by phosphate (PO43–).
This is a big deal because P is not a trace element—it is essential for countless processes that are ubiquitous in biology. Some of the most recognizable are: providing structure for DNA and RNA, and as an essential component of the universal energy “currency” in biology, ATP (adenosine triphosphate). Life cannot survive without those three molecules, and that’s the tip of the iceberg of the essential structures and processes P is needed for to survive. Life as we understood it before this announcement could not survive without P, but we have found evidence that some life may be able to.
It may seem counter-intuitive at first that As could substitute for P because it’s popularly known as a poison. However, toxicity is not a property inherent to any substance; rather it’s always a matter of concentration.6 There is a concentration below which As is not toxic.
One reason As is so effective as a poison is it readily substitutes for P in many molecules essential for biological function, thereby disrupting many biological processes. It readily substitutes for P because it has similar chemical properties to P, which can be inferred simply from a periodic table (both are Main Group 5). Any elements in the periodic table that line up vertically have many similar properties, and are often capable of many of the same types of reactions. But given the fine-tuning—down to single-molecule chemistry—of many biochemical processes, this is enough to block vital reaction pathways.
For another example of how chemically very similar elements or compounds can have vastly different biochemistries due to fine-tuning, see this explanation of potassium ion pumps, which block the smaller but otherwise very similar sodium ion. The same applies with very similar amino acids that have ordinary hydrocarbon side chains—in living creatures, this difference can be crucial, so there are ingenious double-sieve enzymes to separate them.
There is something similar in Group 2: magnesium and especially calcium are vital for life; strontium (below calcium) is tolerable except the radioactive isotopes, while barium (below strontium) and beryllium (above magnesium) are toxic.
It’s a similar reason to why many people speculate about ‘silicon-based life forms’ as a possible alternative organic base to carbon (C)—silicon (Si) is directly below carbon on the periodic table. But silicon is not a good biological analogue for carbon because silicon is a much larger atom, which means that Si-to-Si covalent bonds are much less stable than C-to-C bonds, and Si bonds less well to many other types of atoms. For example, while hydrocarbons and water don’t mix (oil and water), silanes, hydrogen-silicon compounds, react readily with water. Another problem is that while CO2 is a water-soluble gas, SiO2 (silica) is an insoluble solid (e.g. quartz).
Arsenic is a much better analogue for P, but As compounds are not as stable for metabolism as P compounds,7 which is necessary in biology because of the extreme fine-tuning of life and its single-molecule chemistry.8
Why the ET buzz?
Since this discovery provides us with an alternative biochemistry to what we are used to, it supposedly provides more ways that life could arise from non-life both here and elsewhere in the universe. However, GFAJ-1 has not completely done away with P biochemistry. Paul Davies agrees:
“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.”9
However, the original research goes a bit further. The researchers found that GFAJ-1 had a 38% drop in growth rate when fed on As rather than P.10 Moreover, the bacteria fed on As appeared structurally weaker than those fed on P, demonstrated by the robust integrity of the P-fed cells in comparison to the As-fed cells when prepared for analysis.10 Thus GFAJ-1 still grows much faster and the organisms are healthier when fed P rather than As. Therefore GFAJ-1’s utilization of As compounds appears to be a sub-optimal substitute to P biochemistry in GFAJ-1—when P is lacking it can utilize As to grow, but P remains the preferred option when it is available. This is similar in principle to Lenski’s citrate-eating bacteria, which turn out to have a disabled off-switch so that an already-existing citrate-digesting pathway is left on even under aerobic conditions.
Moreover, gamma proteobacteria are a well-known form of earth-based bacteria with some species already known to use As in their biology, so GFAJ-1 is not as isolated from the rest of biology as one might be led to think by the news reports. As big a discovery as this is it still doesn’t break the unity of the biosphere; it merely extends our knowledge of what it can do.
In essence, the “astrobiologists” were merely announcing an earthly experiment in artificial selection (echoing natural selection—which creationists not only accept, but also described before Darwin did). From the researchers’ report,3 we see they moved an existing microbe from a Californian lake to their lab, then gradually reduced the available phosphate, while feeding the culture arsenate. Some microbes in the population had a pre-existing ability to tolerate As—they were the only microbes to survive. If the As-tolerance mechanism was the result of a mutation, it would likely come at a cost. Therefore if these poison-tolerant microbes were returned to the wild, they would be at a competitive disadvantage compared to their wild cousins—see Evolution in a Petri dish?
This whole episode seems like it was a well-orchestrated publicity stunt by NASA to get some attention for itself. While this find is a very important discovery about biology, it’s an important discovery about earth biology at its functional limits. Most biologists won’t abandon a single common ancestor for life based on this find because this is a modification of known biology that operates at suboptimal levels. A better analogy would be so-called “superbugs”, which are deadly in a hospital environment full of antibiotics, but can’t compete with their respective wild types outside of the hospital. This find hasn’t even served to uncover a completely different biology to what we know on earth, much less provide evidence for the existence of extraterrestrial life.
Postscript 1 (10 December 2010): In information just to hand (see http://scienceblogs.com/webeasties/2010/12/guest_post_arsenate-based_dna.php and http://rrresearch.blogspot.com/2010/12/arsenic-associated-bacteria-nasas.html), two Ph.D. scientists have raised serious doubts about the claim that the bacteria in question have an arsenic (rather than phosphate) backbone to their DNA. One of them calls it a ‘big idea with big holes’. The media have widely promoted the claim, which would have reinforced ET ideas in the minds of millions—will they in due course widely publish on these growing doubts? If history is any guide, it’s very unlikely. Notions of ‘alien organisms’ sell papers, whereas being reminded of the fallibility of science (even when dealing with observations on the present-day world) is seen as boring in contrast.—Ed.
Postscript 2 (23 December 2010): Science by media—NASA can give it but can’t take it?
As we remarked earlier, the response from scientific skeptics of the arsenic-eating bacteria “find” was fast and hard-hitting. They pointed out that the methodology was flawed, the predicted chemistry was suspect, and even that there is no reason for GFAJ-1 to evolve the ability to eat arsenic since its environment is one of the most phosphate-rich in the world (see Alex Bradley s and Rosie Redfield s responses). The Lead author, Felisa Wolfe-Simon, has issued a response to the criticisms on her blog, which has in turn garnered further responses from Rosie Redfield (see here and here).
However, NASA employed its usual tactic of silence and “letting it sort itself out in the scientific literature” to play down the criticism:
“When NASA spokesman Dwayne Brown was asked about public criticisms of the paper in the blogosphere, he noted that the article was peer-reviewed and published in one of the most prestigious scientific journals. He added that Wolfe-Simon will not be responding to individual criticisms, as the agency doesn’t feel it is appropriate to debate the science using the media and bloggers. Instead, it believes that should be done in scientific publications.”11
NASA splashes this all over the media, deliberately creating a massive media buzz before the official press conference, and then has the gall to suggest this? If NASA wanted this to be played out in the peer-reviewed literature, they should’ve left it there. Or at the very least, they should not have released a cryptic press statement suggesting this finding “will impact the search for evidence of extraterrestrial life.” But instead, Brown blames the bloggers for misrepresenting the press release:
“The real issue is that the reporting world has changed because of the Internet/bloggers/social media, etc. A ‘buzz’ term like ET will have anyone with a computer put out anything they want or feel. NASA DID NOT HYPE anything—others did. Credible media organizations have not questioned NASA about any text. Bloggers and social media have … it’s what makes our country great—FREEDOM OF SPEECH [emphasis added].”12
Can anyone seriously believe NASA didn’t intend for this to be hyped in the media? Yes, “ET” is a buzz term; but they knew that. Moreover, those “bloggers” include Redfield (she runs a microbiology lab at the University of British Columbia), Bradley (A Harvard biogeochemist—this finding is exactly his research specialty). NASA lapped up the media coverage when it was positive, but once qualified scientists such as Redfield and Bradley, and a dozen others interviewed by science journalist Carl Zimmer (who also gave the NASA researchers opportunity to comment, but they refused to), came out almost unanimously criticizing the findings, they claim the scientists should reserve their comments for the peer-reviewed literature!
It is refreshing to see the criticisms get as much airtime in the media as the self-serving publicity stunt from NASA did because it doesn’t often happen. It also reveals a deliberate agenda by evolutionists to push anything related to evolution (ETs, extrasolar planets, “dinobird” fossils, and Tiktaalik, IDA, ‘Mars life’ on the Antarctican meteorite, just to name a few) onto the public, even at the expense of normal scientific process (e.g. the Archaeoraptor hoax).
- Brown, D. and Weselby, C., NASA sets news conference on astrobiology discovery; Science journal has embargoed details until 2 p.m. EST on Dec. 2, NASA, 29 November 2010. Return to text.
- Brown, D. and Weselby, C., NASA-funded research discovers life built with toxic chemical, NASA, 2 December 2010. Return to text.
- Felisa Wolfe-Simon, F., Switzer Blum, J., Kulp, T.R., Gordon, G.W., Hoeft, S.E., Pett-Ridge, J., Stolz, J.F., Webb, S.M., Weber, P.K., Davies, P.C.W., Anbar, A.D. and Oremland, R.S., A bacterium that can grow by using arsenic instead of phosphorus, Science doi:10.1126/science.1197258, published online 2 December 2010. Return to text.
- Stolz, J.F., Basu, P. and Oremland, R.S., Microbial arsenic metabolism: new twists on an old poison, Microbe 5(2):53–59, February 2010. Return to text.
- Hoeft, S.E., Switzer Blum, J., Stolz, J.F., Tabita, F.R., Witte, B., King, G.M., Santini, J.M. and Oremland R.S., Alkalilimnicola ehrlichii, sp. nov. a novel arsenite-oxidizing halophilic gamma proteobacterium capable of chemoautotrophic or heterotrophic growth with nitrate or oxygen as the electron acceptor, Int. J. Sys. Evol. Microbiol 57:504–512, 2007. Return to text.
- Bergman, J., Understanding poisons from a creationist perspective, Journal of Creation (CENTJ) 11(3):353–360, 1997. Return to text.
- Wolfe-Simon, F., Davies, P.C.W. and Anbar, A.D., Did nature also choose arsenic? International Journal of Astrobiology 8: 69–74, 2009. Return to text.
- Williams, A., Life’s irreducible structure—Part I: autopoiesis, Journal of Creation 21(2):109–115, 2007. Return to text.
- Sheridan, K., New life form found on Earth: Deadly arsenic breathes life into organisms (Update), PhysOrg.com, 2 December 2010. Return to text.
- Wolfe-Simon et al., ref. 3, p. 2. Return to text.
- NASA s arsenic microbe science slammed, CBC News, 6 December 2010. Return to text.
- An arsenic bacteria postmortem: NASA responds, tries to pit blogs vs. “credible media organizations”, Embargo Watch, 7 December 2010. The first comment on the article by Carl Zimmer is also very illuminating—the researchers ignored questions Zimmer asked but answered them when they came from scientists in a lecture. Return to text.
Where does the quote "These bacteria had a 38% drop in growth rate when fed on arsenic rather than phosphorus, and were structurally weaker." come from (no citation…
Thank you for your comments. I didn’t directly quote the study on those points because I merely referenced it. I got the growth rate reduction from comparing the recorded average maximum growth rates of the P-fed bacteria with the As-fed bacteria. For the P-fed bacteria it was 0.86 day-1 and for As-fed bacteria it was 0.53 day-1. For a direct quote, see p. 2 of Wolfe-Simon et al.:
“GFAJ-1 grew at an average μmax of 0.53 day-1 under +As/−P, increasing by over 20-fold in cell numbers after six days. It also grew faster and more extensively with the addition of 1.5 mM PO43- (−As/+P, μmax of 0.86 day-1, Fig. 1A, B) [emphases added].”
So, 1 – (0.53/0.86) = 0.38, hence a 38% reduction in growth rate. For the “structurally weaker” comment, here’s a direct quote from p. 2 of Wolfe-Simon et al.:
“There was variation in the total As content of the +As/−P cells, possibly a result of collection during stationary phase and losses during the repeated centrifugations and washing cycles due to the potential instability of the cellular structures given their swollen state (Fig. 2C, E). In contrast, the integrity of the −As/+P cells appeared robust (Fig. 2D) and thus intracellular P measured for these cells likely reflects their content [emphasis added].”
I hope this helps,
This ‘discovery’ sounds more like NASA is wanting to make sure funding for ‘Astrobiology’ is kept or increased.
It seems that the word ‘Astrobiology’ has just appeared on the table—Study of life in outer space. It makes it sound like there already is life in outer space. How can they have a name for something they haven't directly observed yet?