Frog microbiomes respond well to vaccine for deadly chytrid fungus

Deadly chytrid fungus is killing frogs in huge numbers around the world, and researchers are racing to find solutions.

A US team has been testing a vaccine against the fungus, and has discovered that it can alter frogs’ microbiomes and make them more resilient.

“The microorganisms that make up an animal’s microbiome can often help defend against pathogens, for example by producing beneficial substances or by competing against the pathogens for space or nutrients,” says team lead Associate Professor Gui Becker, a biologist at Penn State University, US.

“But what happens to your microbiome when you get a vaccine, like a COVID vaccine, a flu shot, or a live-attenuated vaccine like the yellow fever vaccine? In this study, we used frogs as a model system to start exploring this question.”

The researchers gave tadpoles non-lethal doses of one of the substances created by chytrid fungus.

Five weeks later, they investigated the tadpoles’ microbiota, to see how they’d changed.

“Increasing the concentration and duration of exposure to the chytrid product prophylaxis significantly shifted the composition of the microbiome so that there was a higher proportion of bacteria producing anti-chytrid substances,” says Samantha Siomko, a masters student who did the research in Becker’s lab at the University of Alabama.

“This protective shift suggests that, if an animal were exposed to the same fungus again, its microbiome would be better capable of fighting the pathogen.”

While the composition and relative amounts of microbes changed post-vaccination, the overall diversity did not.

This is important, because having a less diverse microbiome often leads to frog death.

“Our results are promising because we have essentially manipulated the entire bacterial community in a direction that is more effective against fighting the fungal pathogen without adding a living thing that needs to compete for resources to survive,” says Becker.

The researchers are hoping to learn more about the mechanisms of this microbiome shift, and look at microbiome memory in adult frogs and other animals.

They’re also interested in seeing if different vaccines would have different results.

“It’s possible that vaccines based on mRNA or live cells — like those often used to protect against bacterial or viral infections — may differently affect the microbiome, and we are excited to explore this possibility,” says Becker.

The research is published in Philosophical Transactions of the Royal Society B: Biological Sciences.

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