Last December, NASA announced the discovery of a new life form. But remember how it then turned out that the “new life form” was actually here on earth, and it was just a type of bacterium? Then it arose that the bacterium hadn’t even evolved in the natural world — it had been selected for in an artificial lab setting. And then it turned out that there wasn’t even any concrete evidence that arsenic had actually replaced phosphorous in the bacterium’s DNA, as NASA had claimed?
Well, I don’t remember. And unfortunately, most people don’t either. So in an attempt to set the story straight, The Varsity embarked on four interviews with U of T experts, who each tell a different story. What exactly did go down at Mono Lake? And does this finding have actual implications for life on other planets?
Harald Pfeiffer
Assistant Professor, U of T’s Department of Astronomy & Astrophysics and the Canadian Institute for Theoretical Astrophysics
The Varsity: According to NASA’s website, Wolfe-Simon’s finding of the bacterium that can live in — and, hypothetically, can incorporate into its DNA — high levels of arsenic, “will alter biology textbooks and expand the scope of the search for life beyond Earth.” Do you agree? Or is this just press release hyperbole?
HP: It sounds like press release hyperbole to me.
TV: NYU chemistry professor Robert Shapiro told Salon.com that the discovery of this new strain of bacterium has implications for our search for extraterrestrial life. He says that we should broaden our searches beyond our existing genetic assumptions. Specifically, he told Salon that NASA should shift attention from Europa, a moon of Jupiter, to Titan, a moon of Saturn. What are your thoughts?
HP: In either case, I wouldn’t expect complex life. At best, you might find bacteria. This is because another prerequisite for life [besides the assumed prerequisite of carbon, phosphorus, oxygen, nitrogen, hydrogen, and sulfur] is a temperature gradient, an energy gradient. You need a gradient of hot to cold, of light to dark, to exploit energy. On Earth, these gradients are caused by the Sun. But Titan and Europa are very far away from the Sun.
We think that the bottom of Europa’s ocean may have volcanic vents with enough heat to sustain life, but this liquid ocean is one hundred miles down below the surface [which is a thick layer of ice], and the volcanic vents are probably isolated. Finding that would be nearly impossible.
I would agree that Titan would be a better place to find life than Europa. Titan is cold, but it has a bigger sludge of chemicals. But to find complex life, neither moon would be good. I am much more excited about extrasolar planets.
TV: Why?
HP: Well, we discovered the first extrasolar planet in 1995, and over the last five to 10 years, we have been finding many, like over five hundred. Now, all of these planets are more massive than Earth, because heavier planets are easier to find, and closer to their star than Earth is to the Sun, because a planet with an orbit is easier to find — we don’t have to wait once a year. But it is essentially a matter of years before technology so improves that Earth-like planets are found.
TV: Are any of those five hundred extrasolar planets likely to harbour life?
HP: No; most of them are probably too hot.
TV: Gizmodo reported that scientists in California recently discovered that there are three times as many red dwarf stars in the universe as we previously thought. According to the Gizmodo article, this would add a factor of three to the Drake Equation, tripling our chances of making contact with intelligent extra-terrestrial life. Is this actually the case?
HP: Just multiplying our chances by three is too simplistic, in my humble opinion. Because those red dwarves are much smaller stars than the sun. Now, just because a star is smaller — it still has a habitable zone, but the planets would have to be much closer to their star. And the distance between the red dwarves and their [hypothetical] planets is simply not known.
Still, overall, we have good reason to believe that higher life forms [than bacteria] exist elsewhere in the universe.
Asher Cutter
Assistant Professor, Department of Ecology & Evolutionary Biology and Canada Research Chair in Evolutionary Genomics
TV: Explain in depth your thoughts on the NASA finding.
AC: It’s a testament to natural selection’s power to exploit extreme conditions. But remember that this is something that’s distinct from an independent origin of life, which would be structured in different ways using different biochemistry. This [bacterium] started in the same place, and evolution led to a different solution to its environment.
TV: Would this bacterium be poisonous to ingest?
AC: I can say with confidence that if you eat enough of anything you will die. Also, talk to a toxicologist. This is a slightly complex question. Remember that there are already plenty of bacteria [that have regular phosophate bonds instead of arsenate bonds] that kill you because they’re pathogenic.
Geoff Fucile
PhD, Cell and Systems Biology
TV: Please explain in depth your thoughts on the NASA finding.
GF: Well, they haven’t actually shown that living biological molecules can live with arsenic in place of phosphorus. Phosphorus is essential to life. For example, it constitutes DNA’s sugar-phosphate backbone. Also, phosphate is an important component for regulation in many cellular processes. Signal transduction (how cells communicate with each other) uses an enzyme called kinase, which takes a piece of phosphate from ATP [which are like our bodies’ little batteries] and sticks it on another protein, for example. This can regulate the activity of proteins. This is just one of the important ways that information is propagated within and between cells.
TV: Do you believe that a living organism could actually have, say, a sugar-arsenate backbone in its DNA, or ATA instead of ATP?
GF: I don’t think so. [To prove that they have actually discovered a bacterium with these qualities] would require proof, like some kind of crystal structure from the biological molecules to actually show that they incorporated the arsenic.
It’s important to remember that this was a selective evolutionary study, so they acclimatized the bacteria. What they actually found was bacteria that lived in a low-phosphate environment. That’s legitimate. Then they took it into a lab and acclimatized it to lower and lower phosphate. So that new strain of bacteria was actually evolved in the lab and not found in a natural environment. Still, it is very surprising that the new strain could live in such a low-phosphate environment.
David Guttman
Professor, Department of Cell and Systems Biology
DG: [On Fucile’s comments] Good point. They need to do finer-scale biochemical characterization to find out where exactly the arsenic is being incorporated. It isn’t clear whether this is super exciting or no big deal because, for bacteria, if they have the general ability to carry out a biochemical process or to grow on a specific substrate, it’s generally very easy to select derived strains that can do it better, and that’s really what they did here. The question is whether arsenate has actually taken over the role of phosphate.
TV: Would this be possible to prove?
DG: Yes, probably with some x-ray crystallography.
TV: So why haven’t they already done this?
DG: …Because they wanted to get the paper published before the ink dried?
Experimental evolution is done in hundreds of labs. The key is: if it did make this substitution, then that would be extremely interesting. But the bug still prefers to use phosphate over arsenic, so it has not given up its ancestral abilities.
