A New Twist on Photosynthesis A team of researchers has discovered fungi that "eat" radiation in a twisted version of how photosynthesis happens in green plants. Ekaterina Dadachova, one of the scientists working on the project, talks about the discovery.
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A New Twist on Photosynthesis

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A New Twist on Photosynthesis

A New Twist on Photosynthesis

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A bit later in the hour, we'll be talking about biocomputers and this year's hurricane season. But up first, a discovery that sounds like the plot from one of those 1950s nuclear radiation science fiction movies. Remember them? Well, this one is just as fantastic, but it's real.

Scientists studying the destroyed Chernobyl nuclear reactor were surprised to discover a fungus growing - not just growing; it was thriving on the highly reactive walls of the reactor. Should we be afraid the fungus is going to grow and escape the confine of the reactor and eat everything in sight?

Here's where science comes in. How was the fungus able to not only survive the radiation - how was it able to use it as food? That's what my next guest wants us to know. The research is being published online in this week's Public Library of Science One, and here to talk about it is one of the authors.

Ekaterina Dadachova is an associate professor of nuclear medicine and of microbiology and immunology at Albert Einstein College of Medicine in the Bronx. She joins us today from her office. Welcome to the program.

Dr. EKATERINA DADACHOVA (Associate Professor, Nuclear Medicine and Microbiology and Immunology, Albert Einstein College of Medicine): Hi. Thank you for inviting me, Ira. I am happy to be here.

FLATOW: Well, Dr. Dadachova, tell us about this. How does it survive the radiation? Why isn't it killed by the radiation, and how does it eat it?

Dr. DADACHOVA: Well, it survives for the simple reason that there are doses of radiation inside the reactor in many places where this melanized fungi thrive that are not that high to kill the fungus, because fungi are extremely radio resistant.

I will give you an example. For example, to kill one of the fungi, which we used in our paper, one needs to deliver around one million rads. This is the unit in which radiation exposure is measured. And the dose inside the Chernobyl reactor right now is only approximately one rad per day. So one need to radiate fungi for millions of days. So these doses are really beneficial for them if they can use radiation in their metabolism, but they're are not fungicidal. They do not kill fungi.

FLATOW: We know that fungi, you know, they feast on dead wood and other things. But we never suspected that they feasted on radiation, did we?

Dr. DADACHOVA: No. We never suspected it, but my collaborator, Dr. Casadevall, with whom we do this research, he actually suspected that, you know, fungi can use radiation as energy source when he was reading about this melanized fungi colonizing the destroyed reacting Chernobyl, the soils around it. And later on, we found reports that there are actually findings of melanized fungi in Arctic, in Antarctica, in high elevation. But what actually is in common between all those areas is the lack of other conventional nutrients, nutrients - for example, this deadwood, as you are referring to. So those fungi would be seeking other additional sources of energy, and apparently they will be finding them in ionizing radiation.

FLATOW: Now, the key here seems to be - you have mentioned a couple times -melanin. These fungi have melanin in them.

Dr. DADACHOVA: Yes. These fungi have melanin. Melanin is a pigment. Its name is derived from the Greek word for melanos, which is black. So it is a black to dark brown pigment. And in our experiments, we have shown in several species of fungi that it is actually the presence of melanin which allows those fungi to use the energy of ionizing radiation in their life cycle. If we use controlled fungi, the same fungi but without melanin, they couldn't utilize the benefits of being in the rotation field.

FLATOW: Is this the same kind of melanin that we have on our skin that turn it into darker or makes our skin dark?

Dr. DADACHOVA: Well, melanin is actually a very enigmatic pigment because there is no crystal structure of melanin, no good spectra of melanin, because it is impossible to crystallize it. But it has been shown by many studies that a lot of similarities between melanin, which is found in human skin, in (unintelligible), in hair and in - also in fungi. So it shares a lot of structural similarities.

FLATOW: So does the melanin function in the fungi by absorbing the radiation much like chlorophyll would function in a green plant by absorbing the sunlight?

Dr. DADACHOVA: Well, at this stage, we do not know the mechanism but this is analogy which seems to be correct, because one needs to have a pigment, which serves as a transducer of energy. And that is what chlorophyll does during photosynthesis, transfuse the energy of visible light into the chemical energy the plants are using. And here, it seems to be that melanin is capable of transfusing the energy of ionizing radiation into the chemical energy where fungi are capable to utilize.

FLATOW: Well, let's move ahead and talk about what useful stuff could come out of this discovery.

Dr. DADACHOVA: Well, for example, one can imagine that those fungi or other organisms which are capable of utilizing radiation, they can be used for production of biofuels, for example, now that biofuels is a growing area. But if one start to grow these biofuels on their good lands, you know, that wouldn't be really energy-efficient.

But on the other hand, there are lots of wasted land where, you know, nothing can be grown. There are all this underground storage of radioactive byproducts of nuclear cycles, for example. That's where one can imagine growing all those fungi and using them for biofuel.

Simultaneously, it is possible - now we know that genetic engineering of good crops is going ahead at full speed, so one can imagine that the system will be engineered where there - crops will have gene responsible for melanin in their genome, and they will be able to grow using ionizing radiation instead of visible light, for example. And this could be used in space flights and other application where growing crops conventionally is difficult.

FLATOW: How much radiation do you need? Can it grow in background radiation -and these are higher radiation, as you say - in these nuclear waste sites?

Dr. DADACHOVA: Well, it can grow - we have to actually determine what would be the optimal levels of radiation for this fungi, but it seems that they can be grown in a really broad range of radiation fluxes from something which is tolerable to humans to really high levels, because there are reports and literature that this melanized fungi, for example, live in the cooling pools of nuclear reactors. And over there, the radiation dose is so high that, you know, even this like destroyed reacting Chernobyl is not even getting close to that.

FLATOW: Could we then think about - let's think of something that's out of this world. We're always looking for life in outer space and the harsh environments that are out there.


FLATOW: Could these fungi really be, you know, resistant to not just radiation but other harsher environments that we might look for them in other worlds?

Dr. DADACHOVA: Melanin is known to be a protector of - from, you know, many insults, environmental insults. It protects microorganisms, like when they invade other organism from all this antimicrobial defenses, which the organisms are trying to put up. So melanin can protect against a lot of things, and it is known and it has been actually used in practice that it can absorb very harsh UV rays, for example. And it absorbs all visible light, that's why it is black. So it is possible that those particular microorganisms can withstand a lot of different insults, which they will encounter in the space. Yes, you are right.

FLATOW: Yeah. It's interesting to think, as you say before, of having melanin fungi biomass producers, you know, for energy.

Dr. DADACHOVA: Yeah because, you know, ionizing radiation is everywhere at certain levels, higher or lower, depending on what you are talking about. And it is just wasted. You know, it's being decayed and not used for anything.

FLATOW: Right. Sitting in pools in barrels all over the world.

Dr. DADACHOVA: Yes, exactly.

FLATOW: Does the fungi itself become radioactive and dangerous, one that sits so close to the stuff?

Dr. DADACHOVA: No. Fungi - that's I want to stress, you know, for the listeners - that fungi cannot become radioactive because all they do is they utilize the - for example, gamma radiation, which has been already emitted by radioactive sources.

And what they're doing, they're just utilizing the energy of ionizing radiation. Radiation is energy. It's the source of radiation. That's a completely separate thing. So fungi, just using it exactly in the same manner, as we discussed earlier, the green plants would be using the visible light. So it has nothing to do with fungi becoming radioactive themselves.

FLATOW: Is there enough radiation in outer space that we might grow the fungi in a spaceship if we're going to Mars or some place like that and using them -using it as an energy source?

Dr. DADACHOVA: Oh, yeah. In outer space, there is a lot of radiation. Actually, it is known that radiation exposure of even those who fly on passenger jets, you know, often, they're approaching the radiation exposure of professional radiation workers like myself, for example. So there is a lot of radiation out there for fungi to thrive, yes.

FLATOW: So where do you go from here? What's your next thing - how do you take this one step further?

Dr. DADACHOVA: Well, what we would like to do now is actually to try and figure out the mechanism of this process, because, for example, to figure out the mechanism of photosynthesis, it took the work of several groups and several decades. Well, we hope that, you know, other research groups will become interested in these particular phenomena.

And with the combined effort, we will be able to figure out the mechanism of this fascinating process, which will allow to use it for practical applications sooner than later.

FLATOW: And which was - and basically discovered by accident?

Dr. DADACHOVA: Well, I wouldn't say by accident, because, you know, as I said, this is a collaborative work. And my lab is very interested in using radiation for, say, therapy for different purposes. Dr. Casadevall, who is a prominent microbiologist, she has a long-standing interest in melanin. So at a certain point, you know, these two interests, they, you know, would come together, and they did.

FLATOW: Right.

Dr. DADACHOVA: And, I guess it's now becoming more and more obvious that microorganisms are very flexible and they can use different sources of energy. You see, last year, there was a report that microorganisms live at the bottom of the ocean.



FLATOW: I've got to interrupt because we're running out of time. And this is…

Dr. DADACHOVA: Yes, okay. Thank you so much.

FLATOW: Thank you very much and good luck to you. Dr. Ekaterina Dadachova, associate professor of nuclear medicine at Albert Einstein College. We're going to come back, more science fiction-like stuff. Stay with us, we'll be right back.

I'm Ira Flatow. This is TALK OF THE NATION: SCIENCE FRIDAY from NPR News.

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