The Slime Savior

Frog skin is teeming with bacteria—and some of those microbes might hold the key to fighting the killer chytrid fungus.


Photo: Molly Bletz

Molly Bletz wasn’t lost, exactly, but she could no longer see the lights from anyone else’s headlamp shining through the Madagascan rainforest. She switched off her own for a better look. The inky darkness was filled with the chirps, trills, and clicks of the frogs she was there to collect, but at the moment, Bletz couldn’t detect her own research partners. So she began retracing her steps, trying to ignore the leeches inching up her legs (she’d duct-taped her pant bottoms to her ankles to fend them off, to no avail). Suddenly, she heard a loud Bwoosh! as something huge dropped out of a tree and landed right beside her.

“I just screamed and ran, stumbling in the dark,” says Bletz, a graduate student at James Madison University. She stopped, pulled herself together, and, heart racing, went back to see what had startled her. She found a six-foot-long boa slithering languidly at the base of the tree.

For Bletz, it’s all in a night’s work.

Braving the forests of Madagascar after dark for a month at a time is central to her quest to protect the country’s 400 or so frog species from the deadly chytrid fungus. The pathogen has driven at least 200 of the world’s 6,700 amphibian species to extinction. One-third of those that remain are considered threatened, according to the International Union for Conservation of Nature. And even more than that—40 percent—are declining.

Madagascar houses about 8 percent of global amphibian diversity on an island the size of Texas. Bletz says it is one of the only places in the world the epidemic hasn’t yet hit. She and her colleagues would like to keep it that way, or at least give the animals a means to fight the fungus.

Laboratory experiments have shown that a handful of Madagascar’s frog species are susceptible to chytrid, but there’s a chance that bacteria already living on the amphibians’ skin could be the key to their survival. Bletz, who returned last month from her third expedition to Madagascar, is investigating the potential of inoculating local frogs with probiotics. The idea is to find this so-called “good” bacteria that would be capable of combating the killer fungus.

It might sound wacky, but humans benefit from innumerable probiotic bacteria that check the growth of harmful bacteria and keep us healthy—so why not frogs? Bletz’s advisor, Reid Harris, and colleagues have already shown that the approach can work on mountain yellow-legged frogs in the Sierra Nevada. First in lab tests and then in the field, frogs inoculated with the bacterium Janthinobacterium lividum were able to survive the chytrid fungus epidemic. That bacterium is found on the skin of amphibians in the Western Hemisphere and Europe—but not, so far any way, on Malagasy amphibians. “We’re not going to bring foreign bacteria into Madagascar,” says Bletz. “It’s all about making what’s there better.”

Credit: Photo: Molly Bletz

But first they have to determine which bacterial species make up these local frogs’ microbiomes. Hence Bletz’s nocturnal adventures. Each night she and her team from the University of Antananarivo, Madagascar’s primary public university, capture up to 80 frogs, note the species, swab their bacteria-laden bellies, then release the hoppers. They keep the samples in coolers full of ice packs as they hike on through the forests or mountain grasslands.

Back in the lab, there’s a four-step process to find the super bacteria. Currently, Harris and his team are isolating different bacteria, each of which they will throw into the ring (or in this case, petri dish) with chytrid. Those that reduce the growth of the fungus go on to round two, which launches later this month: Tests to see if the bacterium can grow and survive on living frogs. “Even if we have awesome, killer bacteria, it has to be really good at sticking on frogs or it won’t be of use,” says Bletz. They’ll then test any leading candidates on live lab frogs exposed to chytrid and finally dose a small number of Madagascar’s wild ribbit-meisters in their natural habitat.

Even then, there are still hurdles to overcome. There’s no saying at this point if the researchers will discover species-specific probiotics, or find one or two that work across the frog species. They’ll also have to figure out how to deploy their new bacterial army, perhaps by treating the amphibians’ breeding ponds. And, of course, the scientists will have to make sure that the bacteria don’t aversely affect other wildlife.

In the meantime, Bletz will continue getting to know the forests of Madagascar and its inhabitants, from frog species she’s never before seen to the nocturnal mouse lemurs whose impossibly large eyes shine in the light of her headlamp. And should she encounter another boa? “I’m going to run,” she says.

Frank Vassen
Credit: Photo: Frank Vassen

This article was originally published on onEarth, which is no longer in publication. onEarth was founded in 1979 as the Amicus Journal, an independent magazine of thought and opinion on the environment. All opinions expressed are those of the authors and do not necessarily reflect the policies or positions of NRDC. This article is available for online republication by news media outlets or nonprofits under these conditions: The writer(s) must be credited with a byline; you must note prominently that the article was originally published by and link to the original; the article cannot be edited (beyond simple things such grammar); you can’t resell the article in any form or grant republishing rights to other outlets; you can’t republish our material wholesale or automatically—you need to select articles individually; you can’t republish the photos or graphics on our site without specific permission; you should drop us a note to let us know when you’ve used one of our articles.

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