Genome of frog-killing fungus sequenced

CORNELL (US) — Researchers have sequenced the genomes of 29 strains of a fungus that is responsible for the mass killing of amphibians around the world.

The fungus, Batrachochytrium dendrobatidis (Bd), is older than previously thought—and may have recently spread through global wildlife trade to new locations where amphibians have no immunity, a new study reports.

Previous research had suggested that a group of related strains of the fungus responsible for the current global pandemic, called the Global Panzootic Lineage (GPL), resulted from a recent lethal hybridization.


The fungus infects some 350 amphibian species by attacking and degrading their skin, often causing death. Amphibians began dying off at alarming rates in the 1980s, particularly in Australia and South America, and researchers identified Bd as the culprit in 1998. (Credit: AJC1/Flickr)

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Published in the Proceedings of the National Academy of Sciences, the findings reveal that the GPL existed long before the current pandemic, possibly descending from an ancestor that originated 26,000 years ago.

“We found a lot more genetic variation than people knew about,” says Kelly Zamudio, professor of ecology and evolutionary biology at Cornell University, of the sequenced Bd genomes.

“It could lead us to a better understanding of what makes it kill. Once we know the genetic makeup of a pathogen, maybe we can understand what makes it such a powerful killer.”

The fungus infects some 350 amphibian species by attacking and degrading their skin, often causing death. Amphibians began dying off at alarming rates in the 1980s, particularly in Australia and South America, and researchers identified Bd as the culprit in 1998.

In the study, a sample from Brazil showed the earliest known divergence from that common ancestor. “Early on in the history (of Bd), the Brazil isolate took a different evolutionary path,” Zamudio says.

With the genome sequenced, researchers may now begin to pick it apart and understand which genes are more or less active in causing disease. Though more work is needed, the researchers found variations in genes that secrete peptidases, enzymes that break down proteins, such as skin proteins.

The fungus also has the ability to duplicate certain parts of its genome, but not others, and this replication is greater in the most virulent isolates found in Panama and Costa Rica, where amphibian declines are leading to extinctions.

With the new genetic data, scientists can focus on what recent environmental changes may have played roles in making the pathogen more virulent to its hosts in places where it is endemic and areas devastated by the GPL.

The study provides an example of how modern tools commonly used to understand human diseases may be applied to issues of biodiversity and conservation, Zamudio says.

Researchers from the University of Michigan, the University of California, Berkeley, and the University of California, Riverside, contributed to the study, which was funded by the National Science Foundation, Cornell Center for Comparative Population Genetics, and the Atkinson Center for a Sustainable Future.

Source: Cornell University