How Some Frogs Fight Fungi: Bacterial Buddies

Around the world we are seeing mass populations of frogs go into population decline. Heck, my very first actual blog post was about how a group of frogs in Southeast United States found a way to survive. But it isn’t alone.

When looking at frog populations in the tropics one can find enough data to support the basic fact: Chytridiomycosis appears to be a cool weather disease.  For one, lower temperature on a cold blooded frog leads to a potentially weaker immune system. And for another thing, Batrachochytrium dendrobatidis, the fungus responsible for a large portion of these infections, doesn’t grow as well in temperatures over 25C.  That means frogs living in higher altitudes are more likely to suffer die-offs than those living in the lowlands.  B. dendrobatidis does exist in the lowlands, mind you; it just doesn’t produce the dramatic results.

But, as I briefly touched on in my first post, bacteria also help in warding off the pathogen. A study in PLOS One looks to analyze the bacterium growing on the skin of some persistent members of the frog genus Atelopus.

Surviving Chytridiomycosis: Differential Anti-Batrachochytrium dendrobatidis Activity in Bacterial Isolates from Thre Lowland Species of Atelopus

There are over thirty species of frog in this genus, with all but four facing sharp decline.  One of these remaining species, A. elegans, is standing strong even with B. dendrobatidis being well established in its population. What gives? This little guy should have met his mycelial maker!

A. elegans: I should be dead!

This study looks at the potential anti-fungal bacteria the species harbors, also comparing it to the microbiota of some closely related frogs that don’t appear to be infected with the pathogenic Chytrid. What they did was cultivate and isolate as many bacterial strains from roughly 80 specimens of three species of Atelopus: A. elegans, A. spurrelli, and A. limosus.  This resulted in 148 cultivated strains that were tested for anti-B. dendrobatidis activity.

The isolates of bacteria were streaked on plates which had been diffused with B. dendrobatidis to test for zones of inhibition as well as growth rates of the fungus throughout the dish. Along with each isolate a streak of E. coli was included as a control. E. coli is a bacterium which has been determined to have no inhibitive activity on B. dendrobatidis, and as such would act as a visual comparison of the active bacterial subjects.
After analyzing the growth plates, roughly 40% of the strains isolated from Atelopus elegans showed anti-fungal action.  In both A. spurrelli and A. limosus the percentage of active bacteria was much lower, 19% and 26% respectively.  In addition to the quantities of bacterial strains, this same correlation was viewable in quality of inhibition; two of the three most active strains being only found in A. elegans with the third also being found on A. spurrelli.

This seems to demonstrate that the only species of frog in the study which has tested positive for the pathogen employs a barrage of heavy hitting cutaneous bacteria to increase its resistance to chytridiomycosis.

While it acknowledges that laboratory conditions would differ from host the environment of the host frog’s skin; the research team believes the bacteria isolated in this study, specifically the two members of the Pseudomonas genus (P. tolaassii and P. aeruginosa) that showed strongest inhibitor action, could help combat the fungal pathogen in neotropical habitats as probiotic treatments.



Awesome Reasearchers: Sandra V. Flechas, Carolina Sarmiento, Martha E. Cárdenas, Edgar M. Medina, Silvia Restrepo, & Adolfo Amézquita (2012). Surviving Chytridiomycosis: Differential Anti-Batrachochytrium dendrobatidis Activity in Bacterial Isolates from Three Lowland Species of Atelopus PLOS One DOI: 10.1371/journal.pone.0044832

Photo Cred: Wiki Commons Contributor Phillip Weigell