Gastrotheca excubitor employs bacterial defenses to fight off Bd and the chytrid fungus.
A frog that lives in the east Andes mountains of Peru has been found to be naturally resistant to Batrachochytrium dendrobatidis, or Bd, the fungal pathogen that causes chytridiomycosis, or chytrid, and researchers want to know how.
Researchers from Southern Illinois University Carbondale may have just found a clue as to why the frog, Gastrotheca excubitor, is resistant to the fungus, and it lies in bacteria, and not peptides in the frog, that helps to protect Gastrotheca excubitor from the chytrid fungus. What is also interesting is that a closely related species, G. nebulanastes, was found to be susceptible to the fungus.
“The importance of them being (genetically related frog species) in my research is that despite that, these frogs differ drastically in their response to Bd,” David Burkart, a former Southern Illinois University zoology master’s student, told Southern Illinois University News.
“Understanding what contributes to host resistance is important for informing disease mitigation strategies,” said Alessandro Catenazzi, assistant professor of zoology at SIU. Catenazzi is Burkart’s faculty adviser for the thesis.
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It has been known that frogs have antimicrobial peptides and symbiotic bacteria on their skin that helps to ward off disease, but it is not yet known how Gastrotheca excubitor employs these defenses to fight off Bd and the chytrid fungus.
“We wanted to investigate both bacteria and the peptides to know for certain which were not responsible for providing resistant frogs with protection,” Burkart said. “That’s how we would know where to focus future efforts on understanding what makes resistant frogs resistant.”
Burkhart and his team collected the bacteria and peptides from Gastrotheca excubitor and G. nebulanastes and grew the bacteria to see if they would work to fight Bd. They discovered that the skin of G. excubitor had multiple anti-fungal bacteria on its skin that fought off Bd, while G. nebulanastes had a single, weak bacterium on its skin that fought Bd.
It has been debated in the scientific community whether to employ anti-Bd bacteria applications to stop the chytrid fungus, according to Catenazzi, and it has been determined that bacteria do play a role in containing the fungus and preventing disease.
“The implications of our research extend beyond the amphibian-Bd disease system, as beneficial bacteria are likely important host defenses for other diseases,” Catenazzi said.
Burkart’s thesis will be published in the December 2017 science journal Animal Conservation.
The research received support from the Disney Worldwide Conservation Fund and was a collaboration with Sandra V. Flechas, of the Universidad de los Andes in Bogotá, Colombia and San Francisco State University’s Vance T. Vredenburg.
