A Silver Bullet?
Biologist Reid Harris Seeks to Stem the Tide of an Amphibian Killer
By Eric Gorton
Research technician Mary Alice Simon (left) and senior biology major Emily André collect bacteria from a red-backed salamander as Professor Reid Harris looks on.
Biology Professor Reid Harris might be onto something that could save thousands of lives in some of the most populous parts of the world — the amphibian parts, that is.
His tests in laboratory dishes have shown that bacteria found on the skin of some red-backed salamanders repels a deadly fungus that is being blamed in part for widespread amphibian deaths and even extinction. In late 2004, Australian researchers cited the fungus — chytridiomycosis — as one of the main factors imperiling up to one third of the world’s amphibian populations. Their report also stated that 122 of about 5,700 known species of amphibians, including newts, frogs, toads and some worm-like creatures, had disappeared since 1980.
Even though Harris' research is in its early stages, the initial findings were greeted with great enthusiasm last summer during a symposium on declining amphibian populations. Before his presentation, most of the discussion focused on "finding these chytrids everywhere like Australia, Central America, Western U.S. — and we're finding all these dead frogs." The mood to that point was "gloom and doom," Harris said.
"So then I get out and present the talk and it was just like throwing a match in a can of gasoline. Like here's finally something that might actually work. We still have a lot of work to do, but if you inoculate at-risk populations with some of these beneficial bacteria and so forth … It was pretty exciting. A lot of people were excited about it."
A paper on Harris' research, which involves swabbing an animal's skin and using lab tests to isolate the beneficial bacteria, will be published in March in the journal EcoHealth.
"This particular fungus seems to be a specialist on amphibians’ skin,” Harris said. “It doesn't really go inside, it just lives on the skin ... and if it gets to a certain density on the skin, it seems to kill the adults."
Claude Gascon, a senior vice-president at Conservation International, told Reuters last fall, "The fungus is knocking out species ... It impedes the ability of their skin to absorb oxygen and just suffocates them. It's the equivalent of us ingesting a fungus that takes over our lungs."
The bacterium at the bottom of the Petri dish is clearly effective at fighting the fungus while the bacterium at the top is not.
Harris hatched the idea of using the bacteria to fight the skin fungus while researching another amphibian killer, a fungus that attacks their eggs. Research by other scientists indicated bacteria on some amphibians produced antibiotics against the egg fungus.
"So we were starting to work on that, and are still working on that, then it suddenly clicked that the emerging fungus killing adults was chytrid fungus and that the skin bacteria producing antibiotics against the egg fungus could do the same against the chytrid fungus,” he said.
Working with another scientist at Duke University, Harris was able to create the Petri dish experiment, which clearly shows the bacteria fending off the fungus. For his efforts, Harris has secured a $356,000 National Science Foundation grant to continue the work. He also has spoken at a number of conferences.
"I guess the exciting thing is, it's sort of the beginning of a project and it could be the one thing that might actually help stem the tide of this fungal disease," he said.
With the help of postdoctoral assistant Antje Lauer and his students, Harris is now busy trying to isolate the most effective antifungal bacteria and grow them in the lab. He also is working with scientists at the University of California at Berkeley to see if skin bacteria from mountain yellow-legged frogs, an endangered species native to the Sierra Nevada mountains and the mountains of southern California, can work against the fungus there.
Eventually, the research could lead to a procedure for vaccinating endangered populations, Harris said. Other questions, such as whether bacteria from one species could be used to help another, could be addressed with future research.
Research assistant Antje Lauer looks over a computer display that enables her to separate and group various bacteria according to their gene sequences.
"One thing I have noticed in Australia," Harris said, "is that the (amphibian) groups going extinct are the ones that lay eggs in streams and do not take care of their eggs. None of the ones that brood the eggs declined. So it occurred to me, maybe there's a correlation — the species that brood the eggs have been selected to have the beneficial bacteria for the eggs, so it's in place when the chytrid fungus strikes. But the ones that don't care for their eggs wouldn't have the bacteria to fend it off. There's some tantalizing evidence, enough to look into."
Just how long the fungus has been around is a mystery, Harris said. It wasn't described until 1998. Perhaps it has been around much longer, but went unnoticed until amphibian declines started reaching alarming levels. Loss of habitat, global warming, acid rain and other environmental factors also play a role in the declines of some populations, he said.
A study published in January 2006 in the journal Nature states global warming is responsible for the spread of the fungus. The warming temperatures, according to the study conducted by Latin American and U.S. scientists, are ideal for the fungus.
J. Alan Pounds, the lead author of the study, told the Washington Post, "Disease is the bullet killing frogs, but climate change is pulling the trigger."
Read more about Dr. Reid Harris at http://www.jmu.edu/biology/faculty/harris/harris.shtml. For more on JMU's department of biology, visit the Web site at http://www.jmu.edu/biology/index.shtml.