The Appalachian Mountains are the world’s hotspot of salamander diversity, and home to this Cow Knob Salamander, Plethodon punctatus, from George Washington National Forest, Virginia. (Photo: Matt Becker)
Fighting the fungal diseases that have killed millions of frogs and other amphibians is a top priority, and new research suggests natural soil bacteria might provide protection. UMass Boston biology professor Doug Woodhams tells Living on Earth’s Helen Palmer how they work, and might help other species threatened by these illnesses.
CURWOOD: It's Living on Earth, I'm Steve Curwood. Around the world, fungal diseases have been killing millions of frogs and bats and snakes. And a newly emerging disease in salamanders in Europe is scaring biologists here, so the US Fish and Wildlife Service has introduced a ban on their import to try to protect amphibians in the US. But now scientists see some hope in soil bacteria that get onto the salamanders and frogs and apparently protect them. Doug Woodhams is an assistant professor of biology at UMass Boston, who’s been working with amphibians in Panama – and he explained what his team has found to Living on Earth’s Helen Palmer.
PALMER: Now, you've been looking at the kind of fungal diseases that attack frogs and salamanders and you’ve found some good news.
WOODHAMS: Yes, so some of the amphibians have beneficial bacteria that live on their skin and these have antifungal properties.
PALMER: This is kind of like having good bacteria in your gut, for instance, that stop you from getting sick.
WOODHAMS: Exactly, yeah, so the amphibian skin is a mucosal surface just like our guts and they are also protected by microbiota.
PALMER: Is there any evidence that these good bacteria actually work against these devastating funguses?
WOODHAMS: Yeah there's quite a bit of evidence. Many of the bacteria that we can culture from some amphibian species are able to inhibit the fungus in culture. We also have some population level data that shows populations that tend to have these antifungal bacteria can persist with Bd in the environment and survive.
PALMER: Bd is?
WOODHAMS: Bd is the chytrid fungus that’s been spreading around the world and devastating amphibian populations. So salamanders, frogs, toads. So populations that tend to have more of these beneficial bacteria seem to be surviving, and populations that don't have as many of the individuals that have these bacteria seem to disappear.
PALMER: What are these bacteria? What kind of bacteria are they?
WOODHAMS: We'll they're many different kinds, for example, Pseudomonas is one kind that we find on the skin.
PALMER: That's something that makes people sick.
WOODHAMS: Yeah, there are many different strains and some of them can affect humans, but others are beneficial and they can occur in the water and soil, but they can also occur on the amphibian skin and they produce antibiotic compounds.
PALMER: And you're finding these working? What are they actually doing?
WOODHAMS: With the bacteria they can produce secondary metabolites, so they probably use these in competition with each other, but they also can be antifungal and inhibit the growth of the chytrid fungus. Some of them, what we most recently discovered as I think is one of the more exciting things is that they're producing volatile compounds, so not only compounds that are soluble through the water but things that can be airborne and affect chytrid fungus at a distance. So, for example, one of the Pseudomonas bacteria produces hydrogen cyanide and that's antifungal as well as can kill other organisms as well.
PALMER: Yeah, it's pretty toxic.
WOODHAMS: That's right.
PALMER: It doesn't seem to kill the hosts, the amphibians it's on.
WOODHAMS: That's right it probably doesn't occur in high enough concentrations to affect the amphibians.
PALMER: This is actually as you say very exciting. Is this a kind of approach that could work for other fungal diseases, I mean besides the ones on salamanders and frogs.
WOODHAMS: Yeah it's interesting you mention that because we actually originally heard about a Rhodococcus species of bacterium that was found associated with bats and could inhibit the White-nosed syndrome, and this Rhodococcus was found on amphibian skin so we decided to test it against Bd and it turns out it's also antifungal and can kill Bd.
PALMER: So, the newly emerging variation on the chytrid fungus that seems to be affecting salamanders, Fish and Wildlife has brought in regulations to prevent the import of salamanders from Europe. Do you think these have worked so far to keep the salamander disease out?
WOODHAMS: So far there's no evidence that the salamander chytrid or Bsal, so far there's no evidence that that chytrid has arrived, so hopefully the new regulations will prevent a lot of imports of salamanders and newts from Europe and Asia that might be harboring the fungus.
PALMER: We've seen the chytrid fungus that affects frogs spread all round the world and wiped out massive amounts particularly of certain frogs. If the salamander fungus is not here, then presumably the danger is that once it gets here it will have a similarly devastating effect because they won't have any immunity.
WOODHAMS: Absolutely, and that's why - it may be only a matter of time before it arrives, so that's why there's a recent increase in the concern and research activity trying to figure out which amphibians which salamanders, even frogs may be susceptible - we don't know yet - and especially in Appalachians where it's the world's hotspot of biodiversity. We really want to keep this new salamander chytrid out and if we can't then we need some tools, for example, probiotics or antifungal treatments that may be able to help.
PALMER: How important are salamanders in the ecosystem? I mean, we all love them, they're cute little things, but do they have a really vital role in the ecosystem?
WOODHAMS: They do, and in fact in some areas of the Appalachians, the biomass of the salamanders outweighs even all the other vertebrates combined, and people don't tend to see them but I think they're very beautiful and they often come out at night and so many people don't know that they're even there.
PALMER: So they're really vital in the ecosystem and we run the risk of losing a lot of them should this disease come here. Is there any way to kind of inoculate wild salamanders against it?
WOODHAMS: I'm not sure. It's a possibility but right now I think that the research is really focused on what we can do in a captive setting, whether it's captive raised amphibians that will be re-introduced or maybe things that come in and have to go through a quarantine period. Maybe they could be treated, for example, with beneficial bacteria and then they could go on. But as far as treating wild populations, I think that's more difficult and we need more research to determine if that's going to be effective.
PALMER: But presumably we could work on captive ones in the lab, see what we can make work, and then work out whether there's any way to introduce it. But, yeah, I mean if they have soil bacteria, maybe they're there already.
WOODHAMS: Yeah, absolutely and that's one of things I try to emphasize is that the work that I'm doing I would never want to introduce a new bacterium or a new potential pathogen to an area where it didn't exist before. We want to prevent novel introductions of species, and so what we're working on is finding beneficial bacteria that already exists in populations and either augmenting those populations on susceptible frogs and salamanders or adding it to the habitat where it's already found.
PALMER: So, where does this research go next for you?
WOODHAMS: Well, the next thing we want to try is adding some of these bacteria, not just to petri dishes, but to soil and see if infected amphibians can be cleared of their infection by being housed on soil that's been inoculated with these bacteria. It might even be something...there are these other fungal pathogens so it could be something that you could apply in a cave that could reduce White-nosed syndrome, also rattlesnakes have been recently affected by fungal disease during hibernation so it could be applied into a rattlesnake den, for example.
CURWOOD: That’s UMass Boston biology professor Doug Woodhams, who told Living on Earth’s Helen Palmer about the new discoveries that might help save salamanders and perhaps other wildlife under threat from fungal diseases.
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