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A closeup of a dead frog floating in water with aquatic plants underneath it
A closeup of a dead frog floating in water with aquatic plants underneath it

Chytrid Fungus Deploys Varying Strategies to Infect Amphibians

The ability to activate different sets of genes has likely helped the chytrid fungus Batrachochytrium dendrobatidis spread widely in amphibians, resulting in global population declines. 

A headshot of Tess Joosse
Tess Joosse

Tess Joosse is a science writer based in Madison, Wisconsin. Her work has been published in Science, Scientific American, the Mercury News and beyond. She studied biology at Oberlin College and got a master’s degree in science communication from the University of California, Santa Cruz.

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ABOVE: A dead Peron’s tree frog (Litoria peronii) infected with a chytrid fungus. © ISTOCK.COM, KEN GRIFFITHS

EDITOR’S CHOICE IN MICROBIOLOGY

Since the 1970s, the chytrid fungus Batrachochytrium dendrobatidis (Bd) has spread globally amongst amphibian populations, wiping out entire species and decimating others. Yet while the pathogen, which infects an amphibian’s porous skin and disrupts gas and water exchange, is deadly and ubiquitous, some species are more susceptible than others. Past studies have focused on animals’ immune responses to Bd  infection, but not on how the fungus might be adapting to different hosts. “It was not clear if the fungus itself was doing the same thing in the different species it is infecting,” says María Torres-Sánchez, a postdoc at the University of Florida.

To find out, Torres-Sánchez took datasets from those early experiments and turned them on their heads, looking instead at what genes the fungus was expressing on the skins of different amphibian species with varying susceptibility to Bd. She and her colleagues compared the transcriptomes of Bd growing on 14 species of frogs, newts, and salamanders, and of Bd grown on plates without a host.

While the fungus maintained a consistent set of housekeeping genes, the team found that Bd tailored the expression of other genes to each host, allowing it to pursue multiple infection strategies. For example, in more-vulnerable species, genes essential for attaching to and invading leukocytes, cells that defend a host from pathogens, were upregulated. In more-resistant species, genes promoting quicker reproduction, perhaps to evade or overwhelm a host’s defenses, were elevated.

The results are “really exciting,” according to Amy Ellison, a molecular parasitologist at Bangor University in Wales who was not involved with the study. The list of differently expressed genes could provide “interesting targets” for further studies looking at the mechanism of Bd infection, Ellison adds, or in “identifying populations of amphibians that might be more at risk” for severe disease.

M. Torres-Sánchez et al., “Panzootic chytrid fungus exploits diverse amphibian host environments through plastic infection strategies,” Mol Ecol, 31:4558–70, 2022.

A woman with glasses and a ponytail sits on the ground, holding a frog in one gloved hand while swabbing the animal with the other hand 
María Torres-Sánchez swabs a common coquí frog (Eleutherodactylus coqui) to test Bd fungus gene transcription. 
Sam Shablin


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