Comparative analysis of the skin microbiota and metabolites associated with the neotropical frog, Silverstoneia flotator, in lowland and highland populations
Amphibians are considered as an icon of the global biodiversity crisis. Among the threats to amphibian diversity is the disease chytridiomycosis, caused by the fungus Batrachochytrium dendrobatidis (Bd). The potential use of symbiotic skin bacteria that can inhibit the growth of Bd as a probiotic-based approach to mitigate Bd in wild populations has been gaining interest. However, experiments testing potential probiotics have obtained mixed results, which reflects a need to increase our understanding about the ecology of these symbiotic microbial communities. Given the variation in chytridiomycosis outbreaks across elevations, we aimed to determine how the diversity, structure and anti-Bd function of these symbiotic microbial communities changes with elevation. We collected skin swab samples (N=60) in Panama from three high and three low elevation populations of Silverstoneia flotator, a species thought to be tolerant to Bd. These populations represent a range of environmental conditions, with more dramatic Bd outbreaks at high elevation sites. To assess the skin microbial communities and metabolite profiles, we used 16S rRNA amplicon sequencing of the V4 region and HPLC-MS, respectively.
Our results indicate that across high and low elevations, individuals tend to harbor similar bacterial skin communities, although one lowland site appeared to differ from the others. Interestingly, we found a geographical pattern, with bacterial richness (estimated as the number of Operational Taxonomic Units, which approximates bacterial species) decreasing from west to east. This coincides with the direction of the advancement of Bd through Panama. In addition, the metabolite profiles suggest that there is significant variation among frog populations (i.e. sites) and between elevations. Overall, these results suggest that while the frogs have similar bacterial community structure, the environment might be influencing the function of these communities (metabolites profiles), which might indicate a potential interaction between Bd and the symbionts on its amphibian host that could potentially influence the outcome of infection.