Arsenic-Eating Bacteria Challenge View Of How Life Works

All known life on Earth is made up mainly of six elements — carbon, oxygen, nitrogen, hydrogen, sulfur and phosphorus. Felisa Wolfe-Simon talks about a strain of bacteria described in the journal Science that appears to be able to use arsenic instead of phosphorus in that mix.

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IRA FLATOW, host:

You're listening to SCIENCE FRIDAY. I'm Ira Flatow.

A bit later in the hour, neurologist Oliver Sacks joins us to talk about his new book, "The Mind's Eye," and then we're going to look at the science of brewing beer.

But first, if you were online at all this past week, you may have heard rumors about aliens. Here's what happened. NASA scheduled a press conference dealing with astrobiology and with research to be published in the journal Science. But there were no details. So what happens on the Internet? People start speculating and assuming, and you know what assuming makes out of people.

Well, when NASA finally did have its news conference, it was not about finding life on another planet, but it was sort of about alien life here on Earth. And when I mean alien, it's a life form that had never been seen before, a type of bacterium that does something very unusual.

And, well, rather than me babbling on, let me bring on Dr. Felisa Wolfe-Simon. She's the lead author on that Science paper, and she is a NASA astrobiology research fellow in the NASA Astrobiology Institute at the U.S. Geological Survey in Menlo Park, California. Welcome to the program.

Dr. FELISA WOLFE-SIMON (NASA Astrobiology Research Fellow, NASA Astrobiology Institute, U.S. Geological Survey): Oh, hi, how are you?

FLATOW: How excited are you?

Dr. WOLFE-SIMON: I am thrilled.

FLATOW: Tell us why.

Dr. WOLFE-SIMON: Well, I've been thinking about some time, and what I like to joke is that I've been known for being an exception to the rule myself. And so I think a lot about just being different and what it means to be different. And if you don't know that you're different, then you're normal to you. And so we discovered a microbe, my team and I, that does something different.

So all life we know of I'll back for a moment and remind of something we learned in high school all life we know of requires carbon, hydrogen, nitrogen, oxygen, phosphorous and sulfur. And it uses those elements to make DNA and RNA, so that's like your information technology of the cell; proteins, those are your molecular machines and some scaffolding; and fats and lipids. So that separates you from everything else. So those six elements are required for the three biological pieces in a cell.

The microbe we've discovered appears to be able to use arsenic, if not given any phosphorous, and...

FLATOW: But arsenic kills us. Why doesn't it kill the bacteria?

Dr. WOLFE-SIMON: That's an interesting question, and in fact, that's one of the things that I was really thinking about when I first came up with this hypothesis I published a few years ago.

And just thinking as a biochemist, and arsenic is toxic, arsenate in particular, because it looks like phosphate to your cells, my cells and just about everything else that we can think of.

FLATOW: Ah, so if the cell takes up the arsenic instead of the phosphate, and we say bye-bye.

Dr. WOLFE-SIMON: Basically, and let me give you another example because toxicity I think is in the eye of the beholder. We breathe oxygen, but we know that a large portion of the microbes on Earth, oxygen is toxic. So I think toxicity is kind of an interesting inkling. You know, what's bad for you and I, may not be bad for something else.

FLATOW: Right, yeah, we've heard about these bacteria that live in these hostile places we could never live in.

Dr. WOLFE-SIMON: Absolutely.

FLATOW: And so you discovered this bacteria that has arsenic in it instead of the phosphorous, and that's something that you thought might exist, and you went looking for it?

Dr. WOLFE-SIMON: Yup. It was a simple question. The question is: Is there a microbe on Earth that could substitute arsenic for phosphorous in its basic biomolecules. And so we went to run a very simple experiment, went to the beautiful, incredible lake in Northern California, east of the Sierras, called Mono Lake, which is a very high arsenic environment, also extreme. It's very basic, pH is almost 10, and it's very salty. So it's about three times the salt of seawater.

FLATOW: And so you took some of the muck out of the lake?

Dr. WOLFE-SIMON: Yeah, we took some of the muck out of the lake, and we did a very simple experiment that was driven by that question, and we made an artificial lake water, basically, and we added everything it needs: vitamins, sugars, everything you can think of but no phosphorous.

So that's a typical experiment that might be a negative control. But the added wrinkle was a high dose of arsenic. So someone might ask: How would you come up with such a very strange type of experiment? Well, it was driven by that very simple question: Can a microbe grow using arsenic in lieu of phosphorous in its basic biomolecules.

FLATOW: And you working for NASA have an extra added incentive, because maybe somewhere in the solar system, there might be arsenic instead of phosphate growing someplace?

Dr. WOLFE-SIMON: Absolutely, but I really want to reiterate for us, is that this isn't just about arsenic, and it's just about Mona Lake. It's about a proof of concept, of thinking about science in a little different way.

I think many of us I'm not a mathematician, but I think one plus one is two, and we wouldn't argue with that. But in terms of the biology, you know, exceptions to the rules, often when we first find one exception, there could be more.

So if we can do this one substitution, and my co-authors and I are pretty clear, there is some phosphate in these cells, but it's not enough to account for the growth that we see. And we made a number of different measurements from very different sources and types of techniques in different hands. And it really all points to that where we would only find phosphorous, we also can find arsenic.

FLATOW: So you're saying, then, that you have found the only form of life on Earth that does this. Would that be correct?

Dr. WOLFE-SIMON: As far as we know now. But again, with one exception, how much more might be out there here on Earth and elsewhere in the universe?

FLATOW: Oh, I hear the music. You know, that spooky music, coming on. Oooh(ph).

(Soundbite of laughter)

FLATOW: But, you know, there's that old saying: Extraordinary claims require extraordinary evidence.

Dr. WOLFE-SIMON: Absolutely.

FLATOW: Think you have it?

Dr. WOLFE-SIMON: You know, we went through a number of my co-authors, if you look, it's a laundry list of some fantastic scientists around the United States, actually. And what was interesting, too, an experience, is in astrobiology, so this is the study of life in a planetary context. And I'm a geobiologist. And what does that mean?

So really, the goal is that we have questions. We're going to use any technique from any field to be able to determine what the answers to those questions are. So we use things like mass spectrometry, where we measure the elements in a sample; spectroscopy, we can learn something about the element but also what kind of chemical environment it looks at; and then some what I kind of like to say is old-school microbiology.

You really see just plain growth, and again, with these different techniques all suggesting the most parsimonious way to interpret our current data, is that there is arsenic acting in a very similar way to phosphate.

FLATOW: So if it quacks like a duck, it is a duck. Let's go to the phones, 1-800-989-8255. Brian(ph) in Grand Rapids. Hi, Brian.

BRIAN (Caller): Hi, how are you, Ira?

FLATOW: Hi there.

BRIAN: Good. My question is: Are there any other elements that could substitute like arsenic for phosphorous, maybe another chemical that could simulate carbon or sulfur?

Dr. WOLFE-SIMON: Sure, you know, that's a great question. I think that many scientists well, let me just say I stand on the shoulder of giants, and I'm not the first person to think about life. This is really the first experimental evidence that we could do something different here on Earth in, you know, thinking about how to look for it elsewhere.

But to get back to your question, what's interesting to me is that we look across the periodic table, and we think about we're pretty terrencentric, meaning what could happen on Earth: water, certain temperature, pressure, et cetera.

And I think that there's chemistries that could function in similar ways, depending on where you are on the periodic table. So for example, if we have those six elements on Earth and in those three pieces, in the abstract is that we need to make those three pieces. You need an information storage unit, you need molecular machines and some kind of separation of you from everything else.

Well, we look across the periodic table, let's say given a different chemical environment, temperature, those sorts of things, solvent of life(ph), instead of water, perhaps a different solvent. I think we could come up with a number of different substitutions that might work.

Now again, that's speculative, and I don't want to be too detailed. I have some things I'm interested in pursuing, and I know colleagues of mine around the world probably have some great ideas of what to test next, here on Earth, and to think about how we might look for that elsewhere.

FLATOW: So there's a race on now. You have started the race.

Dr. WOLFE-SIMON: I was hoping, you know, humbly, that I do hearken back, now that we've talked about, kind of alluded to a Saganesque sort of idea; is that, you know, if I can make any contribution, it would be to widen the scope of how we think about biology in this context.

And I'm flattered and honored that there's interest in the work that we've just published.

FLATOW: All right. I have a minute left, and I want to ask you the other question that's on everyone's mind: Are there any planets where this might help find life - that has this kind of structure?

Dr. WOLFE-SIMON: I think absolutely. You know, I've spoken to a number of the people involved, the engineers involved in the Mars lander that's coming soon. It'll be launched shortly, in the coming months. And I think that we can see we might now be able to interpret data differently that we might not have thought of.

So if we're measuring organics, if it's a bit of a different weight because we have, again, a spectrometer, measure weight, well, now we might not throw that out as some maybe artifact.

Ah, so it looks like this, but what we go down a step in the periodic table, or what if we go up? I think that, you know, there's a wide periodic table, and they're making measurements that make that possible. And now we might have a different window, you know, cracking open that door of a different way to think about life as we could recognize it, doing something different.

FLATOW: All right, something to think about. Thank you very much for...

Dr. WOLFE-SIMON: Anytime, absolutely.

FLATOW: Well, we'll have you back. How's that?

Dr. WOLFE-SIMON: That sounds great.

FLATOW: Tell us what extra stuff you're working on. And have a happy holiday weekend.

Dr. WOLFE-SIMON: Absolutely, you, too.

FLATOW: You're welcome. Dr. Felisa Wolfe-Simon is a NASA astrobiologist research fellow at NASA Astrobiology Institute in the U.S. Geological Survey out there in good old Menlo Park.

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