Date of Award


Document Type

Honors Thesis (Open Access)


Colby College. Biology Dept.


Catherine R. Bevier

Second Advisor

Frank Fekete

Third Advisor

Lynn Hannum


Amphibian populations have been declining for several decades, in part due to the emerging fungal skin disease, chytridiomycosis, caused by the chytrid fungus Batrachochytrium dendrobatidis (Bd). Chytridiomycosis has caused extinctions and extirpations in many parts of the world, but its influence varies across species, populations, and individuals. The Green Frog (Lithobates clamitans), which inhabits the eastern half of the United States, seems capable of sustaining Bd infections without experiencing die-offs. It is possible that the Green Frog's epibiotic bacteria are contributing to its defense against Bd as the epibiotic bacteria of several amphibian species are known to play a role in the amphibian innate immune system through the production of antifungal metabolites. This study sampled three populations of L. clamitans in Maine, and screened individuals for the presence of both Bd infection and epibiotic bacteria capable of inhibiting Bd growth. In each population, 25-40% of individuals were infected with Bd, all of which sustained low infection intensities of less than 10 zoospore equivalents. All individuals possessed at least one strain of anti-Bd bacteria. Of the 78 strains of epibiotic bacteria assayed, the metabolites of 72 inhibited Bd growth to some degree, and 38 completely inhibited Bd growth. Three inhibitory bacterial strains were identified through sequencing of the 16S rRNA gene and all were classified as Proteobacteria. The large proportion of anti-Bd bacteria isolated from L. clamitans in this study suggests that epibiotic bacteria likely play a role in defending individuals of the species against chytridiomycosis. In the future, anti-Bd epibiotic bacteria could be used in probiotics as an amphibian conservation strategy.


amphibians, disease, immunity

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