Crisis biology: Can bacteria save bats and frogs from deadly diseases?

As populations plummet, biologists race for a solution.

  • Biologist Vance Vredenburg is one of several researchers turning to microbes in hopes of saving species threatened by disease.

    Anand Varma
  • Vredenburg swabs a Sierra Nevada yellow-legged frog to test for the presence of chytrid fungus in Kings Canyon National Park, California.

    Anand Varma
  • A little brown bat with white-nose syndrome in Greeley Mine, Vermont, March 26, 2009.

  • Dish A shows P. destructans (the fungus that causes white-nose syndrome in bats) spore growth after 21 days. Spores still grew in Dish B with unactivated R. rhodochrous bacteria. In Dish C, activated bacteria completely inhibited spore growth after 21 days. (When this experiment was conducted the, the fungus was named Geomyces destructans; it has since has been changed to Pseudogymnoascus destructans.)

    Christopher Cornelison
 

Page 3

Unlike chytrid, white-nose syndrome has yet to wipe out an entire bat species, and there are still many places in North America unaffected by it. That gives researchers like Tina Cheng hope. If they can identify an anti-white-nose strain of bacteria before the disease hits Western North America, they may be able to blunt its impact.

White-nose syndrome is caused by a cold-loving fungus called Pseudogymnoascus destructans, which grows on bat's wings, faces and tails during hibernation. Irritated, the bats wake from their torpor too often, flying around and expending energy when they should be resting. Eventually, they lose body fat and starve. The disease spreads easily, likely through bat-to-bat transmission, and can kill more than 90 percent of the individuals in a cave.

Thought to have originated in Europe, white-nose was first discovered on American soil in New York in 2006. The disease has spread to 22 states in the Eastern U.S. and five Canadian provinces. It's not clear when white-nose will reach the West, and it will likely act differently when it does, given the region's low humidity and the propensity of some Western bats to hibernate in smaller, more dispersed groups.

Cheng, who was one of Vredenburg's students, originally studied frogs but switched to bats for her Ph.D. "I thought it would be really important to address white-nose syndrome," she says. "Unfortunately for chytrid, it was too late for many species."

She has already identified and cultured a strain of bacteria that seems to slow the growth of P. destructans. Now, she's replicating Vredenburg's experiment on mountain yellow-legged frogs. In Winnipeg last fall, Cheng wiped the bacterium and the fungus on little brown bats collected from a northern Manitoba cave at the start of their hibernation. She then released them into a refrigerator that mimics the cave environment. The bats settled back into sleep and Cheng flew home to Santa Cruz, where she spends hours looking for signs of infection through a camera feed. Sick bats typically live two to three months before dying, but when really ill they will sit alone on the cave floor, shaking. In early February, Cheng said all the bats were calmly hibernating; it was too soon to tell if any were infected.

Eventually, she hopes to develop a bacterial soup that could be misted onto bats as they begin hibernation. "My interest is in prevention for those populations that have not been hit by white-nose," like those in the West, she says. But she's also interested in helping species that have already been affected. "We could prevent species from going extinct."

Research on white-nose has progressed much faster than on chytrid. Only two years after the first New York bats died, scientists had identified P. destructans, linked it to the die-offs, and started looking for ways to combat it. It took years after chytrid was first described for most amphibian biologists to agree that widespread declines were happening and to acknowledge the fungus' contribution. "By the time white-nose came along, people were familiar with a fungal disease affecting wildlife. With chytrid, there was no reference," says Katie Gillies of Bat Conservation International. Still, bat scientists face their own challenges. Because white-nose affects bats at their most vulnerable – while they hibernate – Cheng's proposed spray-bottle application could be as disruptive to bats as the fungus itself.

This disturbance is what Christopher Cornelison, a post-doctoral researcher at Georgia State University, is trying to avoid. Trained as a microbiologist with a specialty in fungi, he isn't interested in the outdoor fieldwork many scientists live for. "The bat people, they always joke that they're going to drag me into a cave and make me do some sampling," he says. He prefers white lab coats, gloves and tidy laboratories, where he's working with the U.S. Forest Service to turn Rhodococcus rhodochrous, a common soil bacterium, into an anti-white-nose weapon – without touching bats.

Cornelison discovered R. rhodochrous through a research group studying how it delayed the ripening of peaches. They noticed that less fungus grew on fruit that had been exposed to R. rhodochrous. Cornelison, who had just begun researching white-nose as a possible dissertation topic, realized the fungus might do for bats what it did for peaches.

R. rhodochrous not only slows the growth of P. destructans, he found, it annihilates it. The bacterium produces volatile organic compounds so potent they can permanently stop the fungus' spores from germinating just by being enclosed in the same chamber together for 12 hours. Now, Cornelison is designing ways for land managers to deploy the bacterium. He's come up with a bacterial paste that can be spread on a plastic sheet, covered with a semi-permeable membrane, and hung in a cave during winter, allowing R. rhodochrous VOCs to escape and kill P. destructans. In the spring, when bats begin leaving caves by day and are at lower risk of infection, the sheet could be removed. Then, says Cornelison, "you no longer have the potential collateral impacts that everybody's concerned about," such as bats dying after being disturbed by well-intentioned humans or the disruption of the cave's microbial community.

Few of these technologies have been field-tested. Still, bat and amphibian researchers feel a sense of urgency that inspires them to work faster, collaborate more, and break down the traditional barriers between microbiology, medicine and field biology. "We have no time to waste," says Vredenburg. With humans spreading germs around the globe at unprecedented rates, "(we need) to figure out what we can do to ameliorate some of the terrible consequences of (an increasingly interconnected) biosphere."

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