Microbes may fight the epidemic driving some frog species to extinction
STRI/DICYT In the past few decades, a lethal disease caused by the chytrid fungus has decimated amphibian populations worldwide, driving some species to extinction. This is in part due to the types of habitats amphibians often thrive in: humid places, favoring the growth of microorganisms. The chytrid fungus in particular also enjoys cool temperatures, so most amphibian species vulnerable to the epidemic inhabit cloud forests.
Yet the chytrid fungus is not the only one enjoying the nice conditions. Countless other microorganisms are present, many of which have made of frog skin their home. For researchers at the Smithsonian Tropical Research Institute (STRI) and INDICASAT AIP, some of these invisible skin dwellers could be doing their hosts a favor, by producing metabolites that inhibit the growth of fungi and other bacteria.
“As a result of evolution, amphibians are expected to possess chemical compounds that can inhibit the growth of pathogenic bacteria and fungi,” explained STRI scientist Roberto Ibáñez.
He is one of the authors behind a paper recently published in Scientific Reports, which explores the compounds on frog skin bacteria as potential antifungal sources for the benefit of humans and amphibians.
Seven frog species were sampled for this study, all inhabiting the Chiriquí highlands in Panama, an area of the country best known for its mountains, rivers and cool weather. For amphibians, it is also a place where the chytrid fungus has caused havoc.
After laboratory analysis, the team determined that the samples taken from frog species Craugastor crassidigitus showed the most promising results. Two bacterial species isolated from its skin exhibited the greatest resistance to the chytrid fungus. One of these also showed strong potential against Aspergillus fumigatus, a fungus affecting humans, especially immunocompromised patients.
Although it was sampled in the highlands, the C. crassidigitus is also found in lowland rainforests, coffee plantations and pastures, warmer areas where the chytrid fungus is not considered a threat to frogs.
Still, these results offer hope. Further research on Panamanian frog skin bacteria may lead to the development of alternative drugs to treat the fungi causing aspergillosis in humans, which are becoming more drug-resistant, and to defy the chytrid fungus epidemic, the major source of disease-related death among amphibians worldwide.
For Ibáñez, who is also part of the Smithsonian Panama Amphibian Rescue and Conservation project (PARC) team –which offers a temporary habitat for the species of tropical frogs most vulnerable to the epidemic– this is just the beginning of this line of research. His colleagues at INDICASAT agree.
“In this study, we are introducing a new family of chemical compounds found in Panamanian frogs that could help amphibians worldwide,” said Christian Martin, the first author of the study along with the principal investigator Marcelino Gutiérrez, both from INDICASAT. “We are also showing to the scientific community a set of possible alternative molecules to fight fungal drug resistance in humans. Although more studies are needed, our collaboration could spark interest in the conservation of amphibians as a novel source of bioactive compounds in humans.”