In recent years, amphibian populations worldwide have seen unprecedented declines. These declines have been associated with a dramatic increase in the incidence of chytridiomycosis. This disease is caused by two fungal pathogens, Batrachochytrium dendrobatidis (Bd) and B. salamandrivorans (Bsal), which infect the skin of amphibians. Previous research suggests that the symbiotic microbial community associated with the skin of some amphibians protects them from Bd and Bsal. In light of these results and the potential impact chytridiomycosis could have on Appalachian salamanders, we characterized the microbial communities of two common stream salamanders, Desmognathus fuscus and D. monticola, and examined interactions between microbes isolated from these salamanders and the pathogen Bd. We completed this by capturing D. fuscus (n=16) and D. monticola (n=11) individuals from a stream in Bedford County, VA. All salamanders were rinsed with sterile water to remove transient microbes and their skin was swabbed to collect microbial cells. Cells were transferred to R2A agar and incubated at room temperature. We identified each unique morphotype by extracting, amplifing, and sequencing the 16S rRNA gene. We co-cultured each isolate with Bd to determine if they inhibit or promote the growth of the pathogen in vitro.
Results/Conclusions
We found that D. fuscus and D. monticola had very similar microbial community compositions and were primarily dominated by the phyla Proteobacteria (61% of isolates), Actinobacteria (18%), Firmicutes (18%), and Bacteroides (3%). These communities were phylogenetically diverse, containing 34 genera of bacteria. The most dominant genus was Pseudomonas. We cultured an average of 16 and 15 unique isolates per D. fuscus and D. monticola, respectively. Very few isolates (2.5%) were able to inhibit Bd in an in vitro challenge assay. This percentage is much lower than reported in previous studies investigating the microbiomes of North American salamanders. The low abundance of antifungal bacteria found in this study suggests that these salamander species may have other defenses against Bd. It is unclear how Bd affects D. fuscus and D. monticola at the individual and population level. However, there have been no reports of drastic die-offs as have been seen in other species affected by chytridiomycosis. Therefore, future research will investigate the prevalence of Bd in several populations of these species.