A northern long-eared bat shows signs of white-nose syndrome, a disease that threatens the species' existence. (Photo: USFWS)
A fungus from Europe is obliterating North American bats, having killed about 6 million in less than a decade and pushing several species toward extinction. But according to a new study, bacteria from the bats' own wings might offer a secret weapon in the battle to save America's flying mammals.
Scientists at the University of California Santa Cruz isolated an array of bacteria from the skin of four bat species, some of which "strongly inhibited" white-nose syndrome, a relentless fungal infection with a mortality rate as high as 100 percent in some bat caves. Published in the journal PLoS ONE, the study identified six bacterial strains that inhibit the growth of Pseudogymnoascus destructans, the fungus that causes white-nose syndrome, including two that suppressed fungal growth for more than 35 days.
"What's promising is that the bacteria that can inhibit the fungus naturally occur on the skin of bats," says Joseph Hoyt, a UC Santa Cruz graduate student and lead author of the study, in a press release about the findings. "These bacteria may just be at too low a level to have an effect on the disease, but augmenting them to higher abundances may provide a beneficial effect."
White-nose syndrome first appeared in a single New York cave in 2006, and has since spread to 25 U.S. states and five Canadian provinces. It only affects hibernating bats, causing them to wake up too early and burn through their fat reserves in winter, when there aren't enough insects to eat. Infected bats can be identified by a white fuzz on their noses, ears and wings, and they seem to die of starvation.
Similar cave fungi exist in Europe, where bats have apparently evolved resistance to their effects. Scientists think P. destructans was brought to North America by humans, possibly spelunkers who unwittingly carried spores on their shoes, clothes or caving gear. The cold-loving fungus can only attack hibernating bats because their body temperatures drop during hibernation in cool, moist caves.
Four American bat species have been hit especially hard by white-nose syndrome, and some regional populations are down 90 percent from their pre-outbreak size. The northern long-eared bat may be suffering more than any other, and many experts warn it's now plummeting toward extinction. The U.S. Fish and Wildlife Service classified it as "threatened" earlier this month, making it the first bat added to the endangered species list due to white-nose syndrome. That will add some protection, but the move drew criticism from conservationists who were hoping for a full "endangered" listing.
"Everywhere the disease has been for a couple of years, this bat is gone," Hoyt says of the northern long-eared bat. "We don't have any tools right now to protect this species."
Ecosystems tend to suffer when any native species becomes extinct, but losing bats could be especially traumatic. That's because they play a vital ecological role by eating huge amounts of insects, including disease-carrying flies and mosquitoes as well as agricultural pests that damage crops. A 2011 study estimated bats save U.S. farmers at least $3.7 billion every year, and possibly as much as $53 billion.
Bacteria found on the wings of big brown bats show promising results in suppressing white-nose syndrome. (Photo: U.S. Forest Service)
There is no cure or treatment for white-nose syndrome, and efforts to slow the spread have been largely limited to cave closures and public education. Entire bat colonies have died out in many places, especially in the U.S. Northeast, and the epidemic is still getting worse in much of the U.S. South and Midwest. Yet at the same time, hints of hope have begun to emerge in some of the hardest-hit areas.
Scientists reported signs of resistance at a few New York and Vermont caves in 2014, for example, including the previously decimated Aeolus Cave in southwestern Vermont. And while the disease can infect nearly every bat in a colony, any bats that manage to survive the winter can apparently clear the infection once they finish hibernating and raise their body temperatures.
The newly identified bacteria could help explain why the disease's effects seem to vary so widely among bat species, Hoyt says. The strains that best suppressed P. destructans came from the big brown bat, a species that has suffered lower mortality from white-nose syndrome than other bats. More research will be needed, though, to determine if bacteria play a role in protecting wild bats from the fungus.
"This study is just the first step in investigating that possibility," Hoyt says. Tests are also under way to see if treating live bats with the bacteria can thwart white-nose syndrome. "We are analyzing data from tests on live bats now," he adds, "and if the results are positive, the next step would be a small field trial."
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