To Bd or not to Bd: Characterizing fungal competition in the amphibian microbiome

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Steve Kutos, Fordham University, Elle Barnes, Berkeley National Lab

Background/Question/Methods
Amphibians, while being critical players in ecosystems across the globe, are being threatened by the rapid spread of a deadly wildlife disease caused by infection with the fungus Batrachochytrium dendrobatidis (Bd). While several studies have shown that certain cutaneous bacteria provide resistance to Bd, little is known about the fungal diversity (apart from Bd) that exists on their skin and what function these microbes serve in their interactions with the pathogenic fungus. To fill this gap, we explored the culturable fungal diversity and function of the skin microbiome of the eastern redback salamander (Plethedon cinereus). Isolates collected from individual salamanders underwent Sanger sequencing at an outside facility after the completion of isolation and PCR amplification using primers that targeted the ITS region was completed. Using Geneious Prime software, we aligned the received sequences to explore the phylogenetic relationships between identified OTUs. Following identification of the isolates, we performed microbial challenge assays with Bd to determine inhibitory potential. We hypothesized that salamanders in the New York area would have a species-rich fungal microbiome that varies in composition by location and at least some of these fungi would be inhibitory to Bd.
Results/Conclusions
Our results suggest a species-rich fungal microbiome with similarities in different locations. The inhibitory ability of some isolates was lower than expected, and some isolates actually promoted the growth of Bd in their presence. The facilitatory and inhibitory abilities of the isolates was more limited than expected, with the most effective in terms of facilitatory function (an isolate identified to be of the genus Penicillium) causing a 30% increase in growth of Bd, and the most inhibitory isolate (Penicillium brevicompactum) resulting in a 27% decrease in Bd growth. The inhibitory ability of each isolate correlated with location rather than phylogenetic distance, suggesting that isolates in the same location were more closely related in terms of anti-Bd function than isolates with the same OTU identification in different locations. Our findings suggest that the role fungi play in the microbial protection of amphibians against pathogens is related to location. In the future, we hope to quantify the complex interspecific interactions between bacteria, fungi, and microbial pathogens.