Nature Podcast

This is a transcript of the 23rd May 2013 edition of the weekly Nature Podcast. Audio files for the current show and archive episodes can be accessed from the Nature Podcast index page (www.nature.com/nature/podcast), which also contains details on how to subscribe to the Nature Podcast for FREE, and has troubleshooting top-tips. Send us your feedback to mailto:podcast@nature.com.

Kerri Smith: This week our skin's resident fungi, friend or foe.

Heidi Kong: We don't know what all of these microbes are doing in and on our bodies.

Thea Cunningham: And a tooth from a Neanderthal child reveals it was prematurely weaned.

Tanya Smith: We could imagine that something may have happened to the mother. Did the mother die? Did the mother move? Was the infant separated? There was something that disrupted the normal process.

Kerri Smith: Plus to the edge of the solar system and beyond with the Voyager mission's chief scientist. This is the Nature Podcast, I am Kerri Smith.

Thea Cunningham: And I am Thea Cunningham.

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Thea Cunningham: When scientists talk about the human microbe biome they usually mean bacteria like the harmless bugs in our guts but our bodies are teaming with another kind of micro organism that gets much less attention – fungi. Heidi Kong, a dermatologist at the US National Cancer Institute and her team are starting to fill in that gap. They took skin swabs all over the bodies of 10 people from behind their ears to the tips of their toenails and sequenced the DNA of all the fungi. Kong told Nature's Ewen Callaway that most of the fungi she found are friendly. Having said that, every year 29 million Americans do develop fungal infections. Here's Kong with more. Nature (2013)

Heidi Kong: Fungi can cause fungal foot infections, for example athlete's foot. We have patients who have fungal toe nail infections as well as at times fungal infections of the hands, some diaper rashes are related to fungi as well. So there are many different types of skin diseases that we do see on a day-to-day basis.

Ewen Callaway: We know fungi cause disease then but do they influence our health in more subtle ways?

Heidi Kong: That is a good question because we don't know what all of these microbes are doing in and on our bodies and it is likely that these are resident microbes that it's possible that they aren't all causing infections that they are likely either sitting there as passengers or they could actually be doing things that are beneficial for human health.

Ewen Callaway: You mentioned that you're kind of interested in filling in this gap, what are the fungi on our skin, so I understand you took 10 people to swab their skin at a bunch of different sites. Then what did you do?

Heidi Kong: So, after we took the swabs then one of the things that was important in our paper was trying to take the fungal DNA out of those swabs. Fungal cell walls are more difficult to break open than say bacterial cell walls. So, one of the important steps in this paper was developing methods to break those cell walls and get to the fungal DNA and then we sequenced the DNA to essentially try to identify the fungi that were present in that sample.

Ewen Callaway: I don't suppose you've come up with a special 'ome name for all the fungi on our skin? Fungome?

Heidi Kong: I have heard one of the terms that I heard use is the mycobiome, m-y-c-o-b-i-o-m-e because scientists who study fungi are called mycologists.

Ewen Callaway: That's very subtle.

Heidi Kong: It's a, you have to listen very carefully in comparing mycobiome versus microbiome

Ewen Callaway: Exactly that could be missed. So you've got this long list of fungi based on DNA sequences. What did you learn about them?

Heidi Kong: So, one of the major things we observed was that we found Malassezia as the primary resident in all of these 11 sites. So, Malassezia is a type of fungus that likes to be in oily areas. In addition to the 11 sites we sampled, we also sampled three sites on the feet. And that one of the things that we were really interested to discover was that there was a lot of diversity, fungal diversity, different type of fungi that are present on the sites that we sampled on the feet. The other 11 sites that we sampled don't tend to have that diversity.

Ewen Callaway: Why would that be?

Heidi Kong: That's a very good question. One of the things that we have thought about is to explain why there's a lot of diversity on the feet is that our feet are exposed to a lot of different environments. We have different types of shoes and we may walk on the floors, different types of flooring in our homes, but it's unclear why the feet may harbour so much more diversity.

Ewen Callaway: I suppose you didn't do a sample where you compared sandal wearers versus people wearing socks and shoes.

Heidi Kong: No we didn't, not for this particular study, but that is a good question.

Ewen Callaway: Are there any hypotheses about what fungi on our body might be doing that's useful?

Heidi Kong: Organisms such as Malassezia which like oil and seem to proliferate quite well on certain body sites especially body sites that we don't want other bad fungal invasive species to inhabit, it's possible that they're preventing other bad fungi from taking hold and causing worse infections.

Ewen Callaway: People are starting to talk about manipulating our microbiomes, faecal transplants are coming into fashion, could we manipulate our mycobiome or the fungus on our skin as well.

Heidi Kong: That's a very good question. It would be very interesting if we could institute a way to modify our mycobiome, so that maybe somebody wouldn't have fungal foot infections.

Thea Cunningham: Heidi Kong talking to Ewen Callaway.

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Kerri Smith: Two space probes both alike in dignity, in the outer solar system where we lay our scene. That's right, the twin voyager space probes are hurtling towards the boundaries of our solar system and it's a journey they've been on since the 1970s. Nature correspondent Alexandra Witze has written a profile of the scientists behind their success. Alex joined me on the line from Colorado. Alex first of all, tell us a little bit about the voyager mission as it was first conceived. Nature 497, 424–427 (23 May 2013)

Alexandra Witze: So, there is a kind of long history to what became the voyager mission in the end. Sort of throughout the 1960s and early 1970s there had been a lot of talk about whether you could send one or multiple spacecraft to one or more of the outer planets, Jupiter, Saturn, Uranus, and Neptune. At one point there was a grand plan for what was called the grand tour of all four planets with multiple probes, that got way cutback with budget cuts and JPL, the Jet Propulsion Laboratory re-invented a shorter slimmer way to go about it. Two probes exactly the same instrumentation, the idea to be redundant if one of them got lost, the other one can still do the jobs and basically the point of the mission was to get at least one of them to Jupiter and one to Saturn, the mission did that and far more of course.

Kerri Smith: And voyager has voyaged almost to the edge of the solar system we hear.

Alexandra Witze: Absolutely, they have done pretty much everything you could do in the outer solar system. So, both of them went together past Jupiter and past Saturn and that's through the late 70s and early 80s and then after Saturn, the mission controller set Voyager-I kind of spinning on a plane out of the plane of the solar system. Voyager II went on to Uranus and on to Neptune and so it too is now out there at the very edge of the solar system.

Kerri Smith: Now they haven't done this on their own and a project scientist who has been involved with Voyager, the entire duration of its mission is Ed Stone, you've written a profile of him for Nature this week, what made you focus on him?

Alexandra Witze: Yeah, Ed Stone is a really interesting guy. He is a very powerful and important planetary scientist and he is the guy when you think of Voyager you pretty much always think about Ed Stone. He has been the project scientist from day one and he talks a lot about how this means that he is the guy who got to decide what discoveries Voyager made and Voyager has done incredible discoveries, it found the volcanoes on Io, Jupiter's moon that has these amazing sulphur volcanoes spewing out. It took incredibly detailed pictures of Europa, the icy moon with these big grooves that may have a subsurface ocean.

Kerri Smith: Let's hear from Ed Stone himself then about being involved in a project like this for so long. I spoke to him earlier this week. He's at NASA's Jet Propulsion Lab in Pasadena, California. The Voyagers have been voyaging since before I was born, I have to say. How do you sort of feel about them, are they a little bit like your children?

Ed Stone: Oh! Very much part of the family, I mean in fact my children grew up with the Voyager, now our grandchildren are growing up with the Voyager, so it's really quite a wonderful 40 years.

Kerri Smith: Apparently there is a little picture of Voyager-I at the Voyager lab and underneath it says “whenever people start to ignore me, I pretend that I have left the solar system.

Ed Stone: Yes, yeah yes, yes, I have seen that one. We've been on the verge of leaving a solar bubble now for several years.

Kerri Smith: So what's the latest?

Ed Stone: Well, the latest is that we are in a new region where all the energetic ions which are inside the heliosphere have disappeared and where we are now seeing what is outside. And our question is, are we still inside connected to the outside or are we indeed outside of the solar bubble for the first time?.

Kerri Smith: You have been involved with this mission from the very beginning and you were a scientist of 30 or 40 at the time?

Ed Stone: Yeah I started as the chief scientist in 1972 and I was 36 years old at the time.

Kerri Smith: And how long will the project sort of last for, I mean I know I am asking you to forecast the future here but I mean will Voyager ever get close to another star as it has been to our own?

Ed Stone: It's very unlikely because space is really very empty and that in the next billion years there is less than a 1% chance that Voyager will have gotten as close to another star as it is to the sun today. Space is really quite empty.

Kerri Smith: When you began the project as a 36-year-old scientist in 1972 how long did you anticipate that this mission would go on?

Ed Stone: Of course when Voyager was launched space age itself was only 20 years old, so it's hard to really extrapolate, we have no idea how long it would take and nor do we know how long the spacecraft would last.

Kerri Smith: That was Ed Stone and back to you Alex, you have been to Ed Stone's office to meet him and also you've been to Voyager mission control what was that like. Because I can't imagine some sort of 1970s, you know, the future of space travel today type set up.

Alexandra Witze: You know I wish I had been able to cover the Voyager planetary encounter back in the 80s because I think it would have been fantastic, there was this great pictures of people and kind of browner with leisure suits in the 1980s looking at these first pictures coming down from the planet. But today mission control is really pretty modest. Mission control is basically a glorified office cubicle and there are about eight full-time engineers who work on the project now and their job is to communicate with the spacecraft. The Voyager's are so far away that to communicate with Voyager I, it takes 34 hours to send a signal at light speed there and back which really to me brought home how incredibly far away these things were. Now Voyager-I is going, you know, literally where no spacecraft has gone.

Kerri Smith: Reporter Alexandra Witze and before her Voyager's Project Scientist Ed Stone. Coming up how Neanderthal tooth can hint at its owner's childhood. But now time for the research highlights read by Adam Rutherford.

Adam Rutherford: In bringing Lake Trout to Yellowstone National Park humans may have inadvertently triggered a cascade of changes with consequences for migratory elk. A team from University of Wyoming in Laramie looked at the long distance effect of introducing Lake Trout to the park in western US. The trout prompted a marked decline in the indigenous trout and unlike the natives the interloper spawn on lake bottoms out of reach of grizzly bears. Earlier research suggested that when the fish are in short supply grizzlies prey on elk calves. The authors used a model to calculate that this dietary shift has cut growth in elk population by as much as 11% even in groups that over winter well outside the park. Until now the decline of this elk is often blamed on the reintroduction of wolves. That study is from the Proceedings of the Royal Society B. Nature 497, 412 (23 May 2013)The identification of a ghost lineage of ichthyosaurs indicates that these extinct marine reptiles were more diverse late in their history than was once thought. Previously only a subset of ichthyosaurs were thought to have adapted for fast swimming in the open ocean and survived in the cretaceous period. Valentin Fischer at the University of Liège in Belgium and his colleagues describe a new species with archaic features. The recognition of this ghost lineage reveals that two distantly related groups of ichthyosaurs lived in the cretaceous. This challenges the assumptions that low numbers and diversity in ichthyosaurs during this period contributed to their extinction and that critter is described in Biology Letters. Nature 497, 413 (23 May 2013)

Kerri Smith: Soon to come, the news chat all about psychiatry's new Bible but now an insight into the life of a young Neanderthal.

Thea Cunningham: We might not remember it but weaning, when we learn to eat foods other than breast milk, is a crucial stage in childhood. It affects how fast and how well an animal develops. Nowadays humans wean their babies much earlier than other apes but how did our ancestors do it? In a paper in Nature, a team gets to grips with when our cousins, the Neanderthals weaned their young. They've studied a tooth from a Neanderthal found in Belgium that died when it was about eight years old. It turns out that the youngster abruptly stopped breastfeeding at 14 months. I called author Tanya Smith from Harvard University to ask her why. Nature (2013)

Tanya Smith: Well it's hard to say for sure, but we could imagine that something may have happened to the mother, you know, either in terms of illness, or you know, transition movement, you know, it's hard to say. Did the mother die? Did the mother move? Was the infant separated? There was something that disrupted that normal process.

Thea Cunningham: And this early weaning supports the idea that Neanderthals grew up faster than modern humans?

Tanya Smith: Well, it would if we felt this is a normal event. So I don't want to give you the impression that we think all Neanderthals would have weaned at 1.2 years of age. I think, in this case, something happened specifically to this mother and infant couple. I don't necessarily think this is true for all Neanderthals. So, what's exciting is now we've got a method we can take to curators and to say, is it possible to study this in other individuals and to look at whether this is a normal pattern, or to look at whether there's a more prolonged period. Certainly by living human standards it's a fairly young age to wean in terms of how traditional contemporary hunter gatherers or even agricultural populations tend to nurse their offspring for longer than 1.2 years. So, whether again this is normal in Neanderthals or whether this is specific to this individual, we won't really know for sure until we look at some additional fossils.

Thea Cunningham: It's fiendishly difficult to tell from fossils when an animal weaned, and Neanderthals obviously aren't around to ask. So the team found a marker of weaning in the child's tooth. Teeth can keep a record of major shifts in diet during childhood because they incorporate various elements from food. One such element is Barium. The team worked out the age of weaning in the child by looking at the levels of barium and they did the same with teeth from human children and macaques. I asked Tania's teammate, Manish Arora in the Mount Sinai School of Medicine in New York why they chose to study barium in teeth.

Manish Arora: Barium is a very special element in the sense that we find very low levels in parts of teeth that are formed before birth. However, at birth the levels rise because breast milk supplies barium to the infant and levels on breast milk are higher than what we find in cord blood. And in modern humans we see that many infant formulas have far higher levels of barium than breast milk, so this provides us with a progressively increasing gradient of barium in teeth which is responsive to changes in diet. And therefore we can use this gradient to reconstruct the timing of exclusive breast milk intake, transitional diet and when breast milk is stopped and the infant is taking entirely a non-milk source.

Thea Cunningham: And how did you go about testing that?

Manish Arora: First of all we studied Macaques. We had data on the time the infant spent on the mother nursing. We also collected breast milk samples from the mother. And we found that the barium distribution in teeth matched very closely with the data that we had collected on the nursing practice. We then went to a human study. This was a very long study that lasted 8 to 10 years, where mothers were recruited during pregnancy and then as breast feeding was happening we had collected the data, and again as in the macaque teeth our model fit almost perfectly in these human beings and showed that barium distribution gave us very good information on the timing of exclusive breast feeding as well as the transition to infant formula..

Thea Cunningham: So, what do these results mean for how humans and Neanderthals developed? We can't conclude from one tooth whether all Neanderthals weaned early. What's more, is weaning alone doesn't determine the length of childhood. But if it were the case Neanderthals weaned earlier, and grew up faster than modern humans could our longer childhoods have given us an evolutionary advantage? Here's Tania again.

Tanya Smith: It's quite possible. We had a number of different innovations occurred in the last two hundred thousand years and it's interesting to speculate that some of those may have been possible because these longer periods of growth and development and longer periods of cognitive processing. We think about the evolution of symbolic behaviour, of more sophisticated tool technology, certainly this is present throughout the world. Perhaps the pressures were off in some way in terms of, you know, needing to spend an entire period of time of your day, you know, in gathering resources and fending off predators, and so there may have been a real social shift that enabled this long, slow childhood.

Thea Cunningham: That was Tanya Smith from Harvard University and before her, Manish Arora from Mount Sinai School of Medicine in New York.

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Kerri Smith: Finally this week, the news chat and we're focusing on psychiatry's Bible. We've talked before about this giant book called the DSM 5. David Adam from Nature's editorial team is here to give us the latest update. Hi David.

David Adam: Hello.

Kerri Smith: Diagnostic and Statistical manual Volume 5 – What is this exactly?

David Adam: Well, it's a very good question. It's been described as the book of vow and it has been described as the Bible of the psychiatric field. It's a compendium of mental illness broken down by different categories of mental illness and different ways that psychiatrists, mainly in America but sometimes elsewhere, used to diagnose the patients who they see in the clinics. So, it's a catalogue of all the different mental disorders that the American Psychiatric Association essentially approves.

Kerri Smith: And the latest revision of this, as the name suggests Volume 5, has just been released this weekend at the American Psychiatric Association meeting but it's been rumbling along for sometimes hasn't it, this revision process.

David Adam: Well, it's been controversial ever since it started early. So the DSM began just after the Second World War, the last revision was in 1980 that was the DSM-4. It's had some particularly low points along its history. At one point it determined sexuality as a mental disorders that came out in the '70s and although these updates tend to come over every two decades, the revision process for the DSM-5 began six or seven years ago. And what they do is they basically cast the net out very wide, they look at all the research, they talk to all the psychiatrists just trying to get a sense of what the psychiatrists are experiencing on the ground.

Kerri Smith: So that's been controversial why, exactly?

David Adam: It was controversial because of the changes they wanted to introduce and then failed to, For example, some people were saying that there should be a new mental illness called Internet Abuse Disorder or Internet Addiction which the DSM has not approved. But what they have done is they've changed the way that autism is diagnosed. So there is a new category called Autism Spectrum Disorder which replaces the previous three or four different types of autism that were already diagnosed, so for example Asperger Syndrome now doesn't exist. People who had Asperger Syndrome are now a part of this; some of them anyway, are part of this broader Autism Spectrum Disorder. And of course everybody has their own opinions on whether those are good changes or not. The broader controversy is that with every different condition that is effectively invented, I mean that they don't make them out of thin air, but they are based on observations of treatment in the clinic. But there seems a new condition and people resent the way, that there is this creeping expansionism of psychiatry into what they think of as everyday life.

Kerri Smith: We've covered those controversies in some depth elsewhere on the podcast over the time over the months and years, ever since this revision has been going on but much more recently one particular problem was thrown into relief by the Director of the National Institute of Mental Health, Tom Insel.

David Adam: Yeah, so he came out effectively damning the DSM saying that the NIMH was going to move in a different direction and actually what he was saying was the DSM is not the right way to guide basic research.

Kerri Smith: And at the moment, for a grant application or any kind of application for money I suppose for research, you are somewhat obliged, at least in the US as a researcher to say, you know, this is the disorder that my research is looking to treat.

David Adam: Exactly. Ultimately it all comes down to if you want to get a drug approved to treat people; it has to treat people who have a certain condition. So, this is the way the system is set up, so the DSM is only ever meant really to be a diagnostic tool used by psychiatrists who see mentally ill people in their clinics but the DSM categories are basically tying researchers' hands behind their back. So, until very recently you couldn't do a research study on psychoses for example, despite the fact that psychoses are a very common symptom of many different mental illnesses. You have to do a study of schizophrenia or of bipolar disorder and the problem there is that you're assuming that those distinctions have genuine biological roots in the way that high blood pressure does, it could be down to certain genes or certain lifestyles. It just isn't the case; the more scientists look for the biological roots of these categories of mental illness the more they discover that actually all these categories overlap.

Kerri Smith: So, from a researcher's point of view then, these are some of the issues you touched on we should mention in a feature that you wrote a couple of weeks ago in Nature and how did the researchers feel that you interviewed about this, I mean, and what potential ways out of this are there?

David Adam: The big problem here is that the current system does not help a lot of people. Part of the problem that is again getting the wrong diagnosis or the diagnosis, as we currently use them, are unsuitable. So if we're going to find better treatment, we need a better diagnoses, to find better diagnoses, you need to do a better research and that's the kind of research which ironically is being held back by the existing system which ironically, is flawed and there's politics at play here because if you start saying, oh, schizophrenia and bipolar disorder don't exist in the scientific sense, in that they're not biologically distinct categories, it's very easy to interpret that as people who're classed as having bipolar disorder, schizophrenia, there's nothing wrong with them that the problems don't exist. Actually what we are talking about is the way they're labelled, the way they're separated. Ultimately the diagnosis is about trying to find ways of treating people, and if you could find ways to treat people without diagnosing them or without labelling them then all the better.

Kerri Smith: That was David Adam. Find David's feature in the archive at http://www.nature.com/news and also on the homepage of nature's news coverage of the DSM this week. We'll be back next week. In the meantime, the second episode of the Nature PastCast has just been published. This time, we travel back to 1985 and the discovery of the ozone hole. I'm Kerri Smith.

Thea Cunningham: And I'm Thea Cunningham.

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