Bacterium used to target frog epidemic
Updated 10:11 pm, Thursday, July 19, 2012
In a push to save thousands of mountain frogs threatened by a deadly fungal epidemic, biologists are treating hundreds of High Sierra tadpoles with an experimental bacterium they hope will preserve the species.
The scientists this week backpacked over Bishop Pass into famed Dusy Basin, 11,300 feet high in Kings Canyon National Park, carrying plastic bottles filled with a purple soup of microbes that could make the infant frogs immune to the dreaded chytrid fungus disease that is spreading swiftly across the amphibian world.
"This is crisis biology," said Vance Vredenburg, an amphibian expert at San Francisco State University who has been researching the epidemic since it was first detected killing countless thousands of mountain yellow-legged frogs (Rana muscosa) in the Sierra Nevada 10 years ago.
If the experiment works, he said, the same microbe could well restore entire populations of the frogs that now face extinction throughout the Sierra.
From his lab in San Francisco on Thursday, Vredenburg followed the expedition led by Cheryl Briggs, a systems biologist at UC Santa Barbara, and Roland Knapp of the Sierra Nevada Aquatic Research Laboratory near Mammoth Lakes.
The team is pouring the bacterial cultures around the shores of two lakes containing hundreds of tadpoles, but no frogs, and around a third lake where barely 100 adult frogs are surviving. All three lakes are infected with the fungus.
The researchers are recording precisely where and how they pour the microbes and watching the tadpoles' behavior before returning home Sunday.
The entire experimental effort has been approved by the National Park Service.
The adult frogs in the lake were first treated with the bacterium two years ago and survived the fungus, Vredenburg said. So the team at Dusy Basin is checking all the adult frogs to see how well they survived this past winter. Next year the team will return to the basin to see how the frogs have fared.
The backpackers are applying the microbe called Janthinobacterium lividum - J. liv for short - to learn whether it can protect the swimming tadpoles against the fungus and allow them to grow, change their form and leave the water as adult frogs.
The bacteria contain a chemical compound called violacein, which appears to penetrate the frogs' skin and confer immunity against the fungus, Vredenburg said.
Successful lab tests
He first tested the effects of his J. liv bacteria three years ago, he said, when he shipped a batch of his Yosemite frogs to biologist Reid Harris at James Madison University in Harrisonburg, Va., where Harris had found that the microbes protected salamanders against the fungus. Those lab experiments worked extremely well with his frogs, too, and they led to the Dusy Basin tests on adult frogs two years ago, he said.
In the epidemic, "zoospores" of the death-dealing fungus, called Batrachochytrium dendrobatidis, infect the frogs' skin, causing the skin to thicken and fall away as the victims die from convulsions.
The chytrid was discovered in Mexico in 1999, according to Vredenburg, and has now swept in waves across every continent in the world - attacking scores of frog species, rendering hundreds of populations extinct. It has attacked salamanders as well.
"It's a devastating epidemic," he said.
Vredenburg returned only last week from researching frog populations in the high-altitude cloud forests of Peru where the chytrid disease has not yet spread, and would have gone to Dusy Basin this week, but he hurt his back hiking the Peruvian highlands, he said.
If more tests of J. liv in the Dusy Basin succeed in immunizing other frog species throughout the Sierra, Vredenburg foresees an even bigger effort. The fungus epidemic has so far not touched the huge island of Madagascar, but its death-dealing blow to frogs there is inevitable, he says.
Spreading the bacteria to Madagascar as a "prophylactic" for protecting the frogs there might be possible, he said.
"It's a really fantastic possibility," Vredenburg said.