New virus found lurking in the genome of deadly chytrid fungus

There’s new hope today for the future of the globe’s amphibians which are being wiped out by a devastating disease.

The fungus Batrachochytrium dendrobatidis, or Bd, causes the amphibian disease chytridiomycosis.

The pathogen causes the disease in susceptible amphibian species through heavy skin infection that can result in death due to osmotic imbalance and electrolyte depletion.

To date, chytrid has contributed to the decline of more than  500 amphibian species and has been linked to 90 possible extinctions.

Now, the first discovery of a virus that infects Bd has been described in a paper in the journal Current Biology, which could have important implications for the development of new research tools to study the fungus and may even hold the potential to one day help control the predator..

The virus, named BdDV-1, was found by chance by researchers working on the population genetics of chytrid to gain a better understanding about where the fungus came from and how it is mutating.

“We wanted to see how different strains of fungus differ in places like Africa, Brazil, and the US, just like people study different strains of COVID-19,” says Jason Stajich, a professor of microbiology at the University of California Riverside, and senior author of the study.

Sequencing the DNA of different chytrid strains revealed the presence of DNA that did not match that of the fungus.

“We realised these extra sequences, when put together, had the hallmarks of a viral genome,” Stajich says. 

Mycoviruses – viruses which infect fungi – commonly have double-stranded RNA genomes. However, BdDV-1 has a single-stranded DNA genome, which is possibly why its presence was overlooked for so long.

The virus has become endogenised – its genome has become incorporated into the fungus’ genome – and is essentially trapped there. Importantly, it appears this only occurred in some strains of the fungus, and the infected ones seem to behave differently to non-infected strains.

“When these strains possess the virus they produce fewer spores, so it spreads more slowly. But they also might become more virulent, killing frogs faster,” Stajich says. 

The researchers would eventually like to clone the virus out of the fungal genome, to see if manually infecting strains of chytrid also results in the production of fewer spores. They also intend to investigate how the virus operates to understand how it infects, to inform future potential efforts to engineer it to help amphibians.

The authors write: “A DNA virus of chytrid fungi may allow the development of viral-based vectors to genetically transform chytrids, a much-needed research tool. [These] viruses also have potential to be used as a form of sprayed biocontrol. 

“Before any efforts to undertake virus-based remediation or biocontrol strategies, it is imperative to know more about the distribution and potential impact of BdDV-1 and related viruses across amphibian hosts and their parasites.”

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