Mr. Toad's Wild Fungi: Fungal Isolate Diversity on Colorado Boreal Toads and their Capacity for Pathogen Inhibition

Area of Science:

• Amphibian biology
• Mycology
• Conservation biology

Background:

• The chytrid fungus Batrachochytrium dendrobatidis (Bd) poses a significant threat to amphibian populations globally.
• While bacterial skin symbionts' roles in Bd resistance are studied, fungal communities associated with amphibians remain under-investigated.
• The Colorado boreal toad (Anaxyrus boreas boreas), a locally endangered species, is susceptible to Bd infections.

Purpose of the Study:

• To characterize the diversity of culturable fungi residing on boreal toad skin.
• To identify specific fungal isolates that exhibit inhibitory effects against Bd.
• To investigate the impact of Bd on the growth and morphology of these associated fungi.

Main Methods:

• Fungal isolates were cultured from boreal toad skin samples.
• In vitro assays were performed to assess the Bd-inhibitory potential of selected fungal isolates.
• Co-culture experiments were conducted to observe fungal growth and morphology in the presence of Bd.

Main Results:

• The majority of culturable skin fungi belonged to the orders Capnodiales, Helotiales, and Pleosporales.
• Five isolates, including two from the genus Neobulgaria and three from Pseudeurotium, demonstrated significant inhibition of Bd growth.
• Fungal morphology generally remained unaffected in co-culture with Bd, though some growth variations were observed with weak statistical support for two isolates.

Conclusions:

• This study expands the knowledge of amphibian-associated fungal communities, particularly on boreal toads.
• Certain fungal isolates possess the capacity to inhibit the growth of the amphibian pathogen Bd.
• Further research with increased replication is warranted to fully elucidate the influence of fungal symbionts on amphibian health and Bd pathogenesis.