April 24, 2024

A virus could help save the world’s amphibians from extinction

A fungus that’s devastating populations of frogs and toads around the world could be vulnerable to a virus that could infect it, and scientists could genetically engineer it to kill it

A deadly fungus that’s devastating frogs and toads around the world may actually be vulnerable to a virus that can infect it. The fungus, Batrachochytrium dendrobatidis also known as Bd or the amphibian chytrid fungus, causes chytridiomycosis in amphibians. This fungus is a pathogen that infects and destroys the skin of frogs and toads, eventually causing heart failure due to electrolyte loss.

Bd causing a global pandemic that has contributed to or led to the likely extinction of 90 species of amphibians, including the Panamanian golden frog, Atelopus zetekior the severe decline of more than 500 species of amphibians.

A team of researchers from the University of California at Riverside recently announced their discovery of a virus that infects Bd. Furthermore, they believe it can be genetically engineered to control or destroy the fungal disease, thereby saving dwindling amphibian populations.

“Frogs control bad insects, crop pests and mosquitoes,” said study co-author microbiologist Mark Yacoub, a doctoral candidate at UCR. “If their populations around the world collapse, it could be devastating.”

In addition to their pest control activities, amphibians are also important indicators of habitat and water quality.

“They are the canary in the coal mine of climate change,” Yacoub explains. “As the temperature warms, the UV light becomes stronger and the water quality deteriorates, which is what frogs respond to. If they are wiped out, we will lose an important environmental signal.”

Although the global decline and extinction of amphibian populations was first noted in the 1970s and 1980s, the cause remained unknown until 1999, when the Bd mold was discovered. The severity of the pandemic began to dawn on conservationists in the early 2000s, when they realized that a disease could pose a primary threat to amphibian biodiversity, leading directly to their extinction.

Given its effects, Mr. Yacoub and his dissertation advisor, microbiologist Jason Stajich, a professor at UCR who studies the processes and mechanisms of evolution in fungi, were excited when they discovered the Bdvirus infect.

“We wanted to see how different fungal strains differ in places like Africa, Brazil and the US, just as people study different strains of COVID-19,” Professor Stajich noted. To do this work, Mr Yacoub, Professor Stajich and collaborators used DNA sequencing technology to study the population genetics of Bd. As they analyzed their data, they noticed some unusual sequences that did not match the fungus’ DNA.

“We realized that these additional sequences, when put together, had the characteristics of a viral genome,” Professor Stajich reported.

The discovery was a surprise. Previously, researchers had looked for it Bd viruses, but couldn’t find any. But this task was quite challenging. For example, by the Bd mold itself living in the laboratory is difficult due to its complicated life cycle and this may be the reason that no viruses were originally detected.

“It’s a difficult fungus to monitor because they have a life stage where they are motile, they have a flagellus, which looks like a sperm tail, and they swim around,” explains Professor Stajich.

Another reason the virus infects Bd what might escape scientists is because it is a single-stranded DNA virus, while most viruses that infect fungi are classified in a different class of RNA viruses, known as mycoviruses. So scientists were looking for the wrong thing. But by studying the genomic DNA sequences of a number of fungal strains, Mr Yacoub, Professor Stajich and collaborators soon discovered that the virus was hiding in the fungal genome.

But the virus is elusive, even if they know what they’re looking for: It’s only present in the genomes of certain fungal species, making it even harder to find.

“Because some strains of the fungus are infected and others are not, this underlines the importance of studying multiple strains of a fungal species,” Yacoub said.

But the virus is infected Bd mold appears to exhibit different properties than molds that are virus-free.

“If these strains possess the virus, they produce fewer spores, which means it spreads more slowly,” Professor Stajich noted. “But they can also become more virulent, killing frogs more quickly.”

Currently, Mr Yacoub, Professor Stajich and collaborators plan to clone the virus to see if they can infect the virus. Bd mold with the clone to see what fungal traits it replicates.

But this surprising discovery raises many important questions. Perhaps most importantly, what molecular mechanisms does the virus use to alter fungal pathogenicity, and can these mechanisms be modified to make the fungus less lethal to amphibians? What is the role of the amphibian skin microbiome itself: are some microbial species more protective than others?

“We don’t know how the virus infects the fungus, how it gets into the cells,” Yacoub said. “If we’re going to develop the virus to help amphibians, we need answers to these kinds of questions.”

In addition to helping Mr Yacoub, Professor Stajich and collaborators learn how fungal pathogens acquire virulence and spread, this research offers hope that science can put an end to this global amphibian pandemic. Furthermore, lessons have been learned from the Bd pandemic may also be useful in addressing the threats posed by other infectious disease pandemics, such as white-nose fungus in bats.

Interestingly enough, though Bd known to infect over 500 species of amphibians, its susceptibility is highly life stage and species specific. For example, the tadpoles of the mountain yellow-legged frog, Rana muscosagenerally suffer from mild sublethal effects, with most mortality occurring at metamorphosis when there is rapid production of new keratinized skin tissue. In contrast, several other amphibian species appear to be relatively tolerant or resistant Bd— including some widespread exotic or invasive species, such as the sea toad, Rijnlla marinaAmerican bullfrog, Lithobates catesbeianusand African clawed frog, Xenopus laevis . This BdResistant amphibians can also provide important clues for the protection of more vulnerable species.


Rebecca A. Clemons, Mark N. Yacoub, Evelyn Faust, L. Felipe Toledo, Thomas S. Jenkinson, Tamilie Carvalho, D. Rabern Simmons, Erik Kalinka, Lillian K. Fritz-Laylin, Timothy Y. James and Jason E. Stajich (2024). An endogenous DNA virus in a fungus that kills amphibians, associated with pathogen genotype and virulence,Current biology 34(6) | doi:10.1016/j.cub.2024.02.062

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