October 25, 2013
White-Nosed Syndrome In Bats Caused By A Robust Fungus
Brett Smith for redOrbit.com - Your Universe Online
A fungus has been decimating bat colonies for at least the last seven years, infecting bats during their winter hibernation, leaving them weak and vulnerable to starvation and secondary infections. Bats infected with Pseudogymnoascus (Geomyces) destructans often have a distinctive white fungal growth around their muzzle, a sign of what is commonly referred to as white-nose syndrome.
In a study published earlier this week by the journal PLOS ONE, biologists from the University of Illinois discovered that the fungus can metabolize almost any carbon source in a cave ecosystem.
"It can basically live on any complex carbon source, which encompasses insects, undigested insect parts in guano, wood, dead fungi and cave fish," said study author Daniel Raudabaugh, a graduate student at the university. "We looked at all the different nitrogen sources and found that basically it can grow on all of them. It can grow over a very wide range of pH; it doesn't have trouble in any pH unless it's extremely acidic."
"P. destructans appears to create an environment that should degrade the structure of keratin, the main protein in skin," he added.
According to the researchers, the fungus has enzymes that metabolize urea and proteins to produce a strong alkaline that could burn the skin. Infected bats are often seen with holes in their skin, which raises their vulnerability to other infections. The biologists noted that the robust fungus can survive on proteins and lipids on the bats' skin, in addition to glandular secretions.
"P. destructans can tolerate naturally occurring inhibitory sulfur compounds, and elevated levels of calcium have no effect on fungal growth," Raudabaugh said.
The only major limiters of fungal growth are temperatures above 68 degree Fahrenheit and the organism’s limited capacity to take in water. While the fungus has trouble absorbing water from surfaces, the presence of degraded fats or free fatty acids, like those found on the skin of living or dead animals, aids it in drawing up water.
"All in all the news for hibernating bats in the U.S. is pretty grim," said study co-author Andrew Miller, who runs the university’s mycology lab and directs Raudabaugh’s research. "When the fungus first showed up here in Illinois earlier this year we went from zero to 80 percent coverage in a little more than a month," he said.
Miller explained that the Illinois team discovered a single infected bat in one cave in the northern part of their state. Several weeks later the majority of the bats in that cave were infected, he said.
While previous research has focused on the fungal genome, Raudabaugh is the first researcher to examine at the basic biology of the fungus, Miller said.
"Dan found that P. destructans can live perfectly happily off the remains of most organisms that co-inhabit the caves with the bats," Miller said. "This means that whether the bats are there or not, it's going to be in the caves for a very long time."