Fighting a Deadly Fungus with Bacteria Harvested from Salamander Skin

Abstract

Emerging fungal pathogens such as Batrachochytrium dendrobatidis (Bd) and B. salamandrivorans (Bsal) have caused significant amphibian population declines worldwide. Healthy amphibian populations are very important indicator species, used in monitoring the health of ecosystems. Rapid decline of these creatures could therefore be highly detrimental to global environmental efforts. A probiotic treatment is the most feasible solution to combat the fungus on salamander skin. In an attempt to develop an efficient probiotic against these infections, we have been conducting research to see what effects the resident skin microbiomes of salamanders have against these pathogenic fungi. We collected 359 skin swabs from wild salamanders in the genera Plethodon, Desmognathus, and Eurycea. A total of 98 bacterial colonies were isolated from 11 skin swabs and grown in pure culture. Thirteen isolates were challenged against Bd on 1% tryptone agar plates. All isolates grew in the presence of Bd, but those species either did not form measurable zones of inhibition, or the zones produced were masked by bacterial motility. The isolates that did not form measurable zones of inhibition have been discounted as candidate probiotics. In future screens, we will retest the samples that were masked by bacterial motility. We expect other isolates will inhibit fungal growth, and we will recommend these isolates for therapeutic treatments of diseased amphibians. By identifying native salamander bacteria with antifungal properties, it is possible to give our salamander populations the means to resist this deadly threat.