More than a decade after the Maryland Zoo in Baltimore was approved to establish a captive population of adult Panamanian golden frogs (Atelopus zeteki) to get them out of the path of the deadly fungal disease Batrachochytrium dendrobatidis (Bd), only ghosts of the black-spotted yellow beauties now haunt the riverbanks of western Panama. But while captivity has been the species’ only defense from extinction, it may also be fundamentally altering the animals in ways scientists are striving to understand.

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[/text_output][text_output]Dr. Matt Becker, a postdoctoral researcher at the Smithsonian Conservation Biology Institute who has focused his research on the use of probiotics to help frogs fight off Bd, is among those ranks. In 2011, he set out to determine whether eight years in captivity could change the diverse bacterial community found on the skin of amphibians that act as a first line of defense against pathogens.

What he found surprised him.

“After eight years in captivity and even after one generation, 70 percent of the bacteria on their skin was the same as it was in the wild,” Becker says. “It was more than I expected. There were some obvious differences, but if they’re maintaining that much of their microbial community, that’s a good sign.”

Becker published his findings recently in Biological Conservation, adding to a growing body of knowledge related to the microbiomes of animals, including humans. Researchers are interested in learning more about how probiotics—or beneficial bacteria—confer health benefits to the hosts on which they live. Probiotics are used in agriculture and aquaculture, and even in human medicine.

For Becker, probiotics may also be the key to someday putting the frog species most susceptible to Bd—like the golden frog—back into their native habitat. In one study, Becker and colleagues successfully transferred probiotics from the Four-toed salamander (Hemidactylium scutatum), which can effectively fight off Bd, to the Mountain yellow-legged frog (Rana muscosa), giving the frog the anti-fungal properties necessary to survive the disease.

While treating every frog in the wild with probiotics may be unrealistic, Becker says probiotics could be the key to returning captive populations to the wild. The probiotics method could also help prevent epidemics before they spread in places like Madagascar, where chytrid was recently detected.

“There are a number of different potentially effective disease mitigation strategies that could work together with a probiotic biotherapy,” says Reid Harris, the ASA’s director of international disease mitigation and one of the first scientists to look at probiotics as a potential defense for amphibians against chytrid. “But for now the probiotic biotherapy is the only field-tested method that has worked to mitigate the disease threats.”

In recent probiotic trials with the Panamanian golden frog, the results haven’t been as encouraging, however. Becker has tried five different probiotics that don’t seem to colonize the skin of the frogs, either because the frogs themselves or the bacteria on their skin are inhibiting the bacteria from colonizing. Becker’s ongoing studies at the Smithsonian Conservation Biology Institute aim to identify why some individuals are able to survive the pathogen—whether it has to do with probiotics, with genetics, or with a combination of the two—and why others succumb to the disease.

Becker’s finding that Panamanian golden frogs retain 70 percent of their microbial community in captivity will help him find the right kind of bacteria to transfer to the golden frog—one that will persist both in captivity and in the wild. And ultimately it serves as a reminder to animal keepers and collection managers that they should do whatever they can to protect the frogs’ microbial community. This could include using the same soil and other elements from the animals’ natural environments. Recent studies have shown that 16 to 90 percent of bacteria are shared with the amphibian’s surrounding environment.

“I don’t think many people think about what’s going on with an animal’s microbiome when we bring them into captivity,” Becker says. “But we have to think not just about preserving the genetic diversity of these captive populations, but about their microbial communities, too. If we’re affecting the microbial communities dramatically, this may have consequences down the road.”

Becker says when he started researching probiotics with Reid Harris in 2006, very little was known about the microbiome of amphibians. Now he hears about new people working on probiotics every month, he says. This, combined with research into potential vaccines and genetic resistance—gives Becker hope that his favorite species—the Panamanian golden frog—may someday return to its riverbanks.

“The more people we have working on a solution, the better,” Becker says. “Maybe the solution doesn’t end up being probiotics. I really don’t care what the solution is, as long as we can stop the spread of Bd and get these guys back in the wild. It breaks my heart that they’re not out there anymore.”

By Lindsay Renick Mayer

Photo: Matt Becker prepares a probiotic bath for Panamanian golden frogs. Photo © Brian Gratwicke, Smithsonian Conservation Biology Institute. [/text_output][/vc_column][vc_column width=”1/3″]

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Anti-fungal bacteria that are applied to frogs to see if they can ‘stick’. Photo © Brian Gratwicke, Smithsonian Conservation Biology Institute.

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Panamanian golden frog in a probiotic bath. Photo © Brian Gratwicke, Smithsonian Conservation Biology Institute.

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