How purple bacteria could help save amphibians in the Rockies

A Colorado researcher is using boreal toads’ microbiomes to help them ward off a deadly fungus.


Browns Creek slips out of the Collegiate Peaks near the central Colorado towns of Salida and Buena Vista. Bordered by conifer forests and alpine wetlands, the waterway offers perfect habitat for an obscure amphibian called the boreal toad, a warty, mottled creature about the size of a human palm. Historically, boreal toads abounded in Rocky Mountain streams above 7,000 feet, but in the past several decades, populations have plummeted. 

Habitat destruction, pesticides and non-native species all play a role, but the toads’ biggest killer is a fungus called chytrid, or Batrachochytrium dendrobatidis. Chytrid has had a devastating impact on biodiversity worldwide: It’s responsible for the collapse or extinction of some 200 species of amphibians. “Amphibians are one of five classes of vertebrates on the planet,” explains University of Colorado conservation biologist Valerie McKenzie. “What if there was a single virus affecting squirrels and whales and people and pandas and coyotes across the board? We’d be freaking out. That’s what people in the amphibian world are feeling.”

Efforts to save amphibians range from scouring ponds with chemicals to creating an “amphibian ark” to petitioning the federal government to list species as endangered, as the Center for Biological Diversity did for the southern Rocky Mountain population of the boreal toad in 2011. But the feds have until 2017 to issue a decision, and in the meantime, chytrid is creeping deeper into the mountains. In 2014, it was discovered in the streams and wetlands of the Collegiate Peaks, long a refuge for boreal toads. Toads there are now in critical danger of going extinct.

Yet even if the toads gain federal protections, the government can’t save them from an insidious fungus that spreads by uncertain mechanisms. Valerie McKenzie, however, thinks she can. 

A juvenile boreal toad in New Mexico
Flickr user J. N. Stuart

About a decade ago, McKenzie read a paper identifying a type of bacteria called Janthinobacterium lividum, which lives on red-backed salamanders’ skin and seems to inhibit the effects of chytrid. She wondered whether boreal toads had similar bacteria in their microbiome, and whether it could be somehow manipulated to ward off the fungal disease. 

Twelve hundred miles away, biologist Vance Vredenburg of San Francisco State University was asking similar questions about the microbiomes of mountain yellow-legged frogs. Independently, both scientists began conducting experiments. In California, Vredenburg found that frogs with J. lividum on their skin survived chytrid infections, while those without it died. In her lab in Boulder, McKenzie noted the same results with boreal toads. 

But neither scientist was comfortable releasing J. lividum into the wild, because they worried about “inadvertently spawning a new biological threat,” as HCN reported in 2014. That threat would be eased if scientists could find a hyper-local strain of the microbe to grow in a lab and release in local populations, but that process could take years. 

Finally, last summer, one of McKenzie’s students isolated a native strain of J.lividum from the skin of boreal toads in the Collegiate Peaks. Soon, McKenzie was growing the bacteria in her lab — bright, violet-colored cultures that streaked and blobbed across her petri dishes. She began calling the project Operation Purple Rain. 

Now, armed with plastic totes, spray bottles filled with bacteria, and a boom box playing Prince on repeat, McKenzie and her team are preparing to unleash Operation Purple Rain into Browns Creek. In August, Colorado Parks and Wildlife is releasing thousands of tadpoles into the Collegiate Peaks, and McKenzie and her team will be close behind to collect the baby toads, spray them with J.lividum and release them back to the wetlands with a small, neon-colored spot on their feet. Later, she will return to the mountains to see whether toads that were treated have a higher rate of survival than those that weren’t.

Vance Vredenburg doesn’t work with McKenzie, but he believes her research could help save amphibians, in the Rocky Mountains and beyond. He tried a similar experiment with mountain yellow-legged frogs in a Sierra Nevada pond, and preliminary monitoring showed that adult frogs treated with the bacteria were better able to survive chytrid infections. “My interpretation is that the J.lividum bought them time to mount their own defense,” he says. “We may have slowed down the dynamics of the pathogen.” Vredenburg hopes to publish a paper on his research soon, but the work is currently halted: The year after he dosed the frogs, California’s drought caused the pond to dry up entirely, killing off the local population. 

For now, Vredenburg has re-focused on lab work. He’s studying the Wyoming toad, which has been extinct in the wild since 1994. Biologists have repeatedly re-introduced captive-bred toads to Wyoming’s ranches and wild areas, but the animals have never survived. Vredenburg suspects chytrid is to blame. He’s trying to determine whether toads that are infected with the fungus in his lab and artificially “saved” with a small dose of an anti-fungal chemical are then able to form their own natural defenses against chytrid. If they are, Vredenburg hopes to inoculate Wyoming toads with the disease and release the newly adapted creatures into the wild next summer. 

Though both scientists’ work could indeed have unintended consequences, McKenzie believes the risk is low. After all, the strain of J.lividum she’s introducing to Browns Creek is already native to the ecosystem — she and her team are simply manipulating it to help the boreal toads make it through their most vulnerable life stage. “As they change from tadpoles to toads, they’re passing through the eye of the needle,” McKenzie says. “We’re just going to temporarily boost bacteria that’s already native to this system, to get the toads past that critical stage.”

Krista Langlois is a correspondent with High Country News. 

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