HANNIBAL, Missouri––Going bananas may save North American bats from white nose syndrome, a fungal disease known to have killed 5.7 million bats since arriving from Europe circa 2006.
More precisely, researchers studying a common bacterium that delays the ripening of bananas have discovered that it also kills fungi common to bananas and the white nose fungi.
Joining forces to test the use of the bacterium to treat bats, a team including representatives of Bat Conservation International, The Nature Conservancy, the U.S. Forest Service, and Georgia State University graduate students during the third week of May 2015 returned 75 apparently healthy bats to the wild at the Mark Twain Cave Complex near Hannibal, Missouri.
The bats were the first known to have recovered well enough from white nose syndrome to be released.
Explained Nature Conservancy “Cool Green Science” blogger Matt Miller, “When researchers at Georgia State University began studying the common bacterium Rhodococcus rhodochrous, they were not thinking about bats. They were not even thinking about fungi. They were thinking about fruit. When bananas, peaches and other fruit are picked, the plants emit their own chemical signals. These begin the fruit’s ripening process.
“When fruit has to be delivered thousands of miles to supermarkets––as is so often the case––it’s a race against time. The fruit can ripen and rot before it makes it to the store’s shelves,” Miller wrote.
“Researchers were investigating the effectiveness of volatile organic compounds emitted by Rhodococcus rhodochrous in delaying ripening in fruit. Researchers and graduate students began noticing another effect of these volatile organic compounds: fungus inhibition. The fruits exposed to the bacterium were not getting moldy.
From going bananas to going bats
Recalled Georgia State University doctoral candidate Chris Cornelison, “I was standing there looking at a bucket of moldy bananas next to a bucket of bananas with no mold. If the bacterium could be so effective on fungi on bananas, could it have similar effects on fungus on bats?”
Exactly how the white nose fungus kills bats was then still unknown, but visible symptoms of the white nose syndrome had been recognized since 2008: fungal spores and lesions appear on the skin of the muzzle, ears, and wings of infected bats, who often move toward the cold mouths of caves instead of remaining in colonies, and attempt to make feeding flights in winter, finding no insects to eat but exhausting their fat reserves. Some infected bats even seek food by daylight, contrary to their normal nocturnal habits. Infected bats eventually either freeze or starve to death.
Fungus disrupts hibernation
University of Wisconsin and U.S. Geological Survey National Wildlife Health Center scientist Michelle Verant in January 2015 published findings confirming the longtime hypothesis that white-nose syndrome kills bats by causing them to burn excessive amounts of stored energy during the hibernation season.
Verant and team compared the amounts of energy used by infected and uninfected hibernating bats, as indicated by proportions of lean tissue to fat. The exercise also discovered, Verant wrote, that “Clinical signs are not the start of the disease; they likely reflect more advanced disease stages.”
The 75 bats who were treated and released at the Mark Twain complex already exhibited visible symptoms, but not so severe that they were deemed incapable of recovery. The bats were captured in fall 2014, put in mesh bags near plates containing the Rhodococcus rhodochrous bacterium, and left there for 24 to 48 hours before being moved to an enclosure in a natural cave hibernaculum, where they spent the winter.
Then, said U.S. Forest Service plant pathologist Daniel Lindner, “We tested for their fungal load and compared that to the fungal load when we first captured them. The bats had no detectable signs of white nose syndrome and could be released,” except for some whose wing damage was believed to be so severe that they could not survive in the wild. These bats were kept as “conservation ambassadors.”
In theory, Rhodococcus rhodochrous could be introduced to caves wherever white nose syndrome has been discovered, or is deemed likely to spread. But the application technique must be improved.
“In this trial, we had to touch every single bat,” said Katie Gillies, director of the Bat Conservation International imperiled species program. “The goal,” Gillies explained, “is to optimize this tool so that we can treat a large number of bats without touching them.”
The most promising approach, suggested Lindner, would be to use a device that he described as “A very sophisticated version of a commercial-grade air freshener, like what a hotel might use.”
But, cautioned Lindner, “We have to make sure it’s not going to upset each cave’s delicate ecology,” by killing native fungi as well as the white nose fungi.
Lichen might also be harmed. Scientifically defined as “a composite organism that arises from algae or cyanobacteria (or both) living among filaments of a fungus in a mutually beneficial relationship,” lichen thrive in many habitats, including caves and inside solid rock, that are inaccessible to other organisms. Lichen are believed to be among the oldest life forms on earth, and some lichen are believed to be among the oldest individual living beings.
Observed Nature Conservancy blogger Miller, “This is why fungicides have not been used to fight white nose syndrome; they typically kill all fungi, not just the harmful species.”
Lindner is not optimistic that Rhodococcus rhodochrous alone will be the “magic bullet” that stops the white nose syndrome pandemic and saves North American bats from the deadly fungus.
“This is one tool, but we will need many more to manage this disease,” Lindner said. “But tools like this could buy time for bats to adapt to the disease and develop resistance. That could prevent extinctions and allow healthy bat populations to rebound.”
The fungus causing white nose syndrome is Pseudogymnoascus destructan, formerly called Geomyces destructans. It kills up to 99% of the bats it infects in North America, but “does not have the same mass mortality effect on European bats as it does in North America. Indeed, native European bats seem to have a resistance resulting from coevolution with the fungal pathogen,” reported Sebastien Puechmaille, Ph.D., of the University of Greifswald, Germany, in a recent posting to the ProMED-mail listserv maintained by the Program for Monitoring Emerging Diseases, and in a paper scheduled for publication in the peer-reviewed journal Current Biology.
“This was another key factor in suggesting Europe was the origin of the Pseudogymnoascus destructan fungus,” said Puechmaille. “Our study paves the way for future research to uncover the exact site of origin in Europe, information that would likely shed light into the exact nature of the human activity responsible for the introduction” of Pseudogymnoascus destructan to North America.
Observed Stefania Leopardi of the Royal Veterinary College in London, England, “Hibernating bats in North America are mostly insectivorous and have fundamental roles in insect control, pest control and plant pollination. White nose syndrome might then disrupt a fragile equilibrium with ecological consequences well beyond the loss of a single species.”
An example might be the influence of bat abundance on fireflies.
Virginia Military Institute assistant biology professor Paul Moosman Jr. discovered in 2009, with National Science Foundation sponsorship, that fireflies are highly toxic to bats, who hunt mainly by echolocation. Moosman reported his findings in the journal Animal Behavior.
“I believe it is quite possible that bats would attempt to eat fireflies, especially if the firefly was not flashing,” Moosman told Jennifer Viegas of Discovery News. Instead, Moosman learned through scat studies, bats rarely ingest fireflies, who emit “a burst of flashes” when a bat swoops nearby.
“Bats don’t always catch insects directly in their mouths,” Moosman explained. “They often catch them with their wing or tail membrane, then scoop them into their mouths. They also sometimes have to make more than one pass to catch an insect. So there may be plenty of opportunity for fireflies to respond to a bat once they’ve felt a physical disturbance, but before being chewed up.”
However, coincidental with the decline of bats throughout the Northeast, Southeast, and Midwest due to white nose syndrome, fireflies are widely believed by casual observers to be also in decline. Are fireflies really fewer, or just flashing less often because fewer bats are about?
Clemson University scientists Alex Chow and Juang-Horng Chang founded the Vanishing Firefly Project in 2010 to try to find out, with the help of volunteers throughout firefly habitat. After nearly seven years, however, their data remains inconclusive.
Meanwhile, white nose syndrome continues to spread west. The Oklahoma Department of Wildlife Conservation acknowledged on May 15, 2015 that the fungus causing white-nose syndrome had been found in three tri-colored bats in a privately owned cave in Delaware County. The bats were not yet visibly ill.
Noted ProMED, “Oklahoma is the westernmost state where fungus has been found and is the third state where the fungus is confirmed, but the disease is not present.”
A month earlier, on April 17, 2015, Iowa Department of Natural Resources endangered species coordinator Kelly Poole told media that three bats collected in Des Moines County had been found to have white nose syndrome, the westernmost point at which it has been confirmed.