Fighting fungi with fungi: the mycobiome contribution to emerging disease in amphibians

30 31 Emerging infectious diseases caused by fungal taxa are increasing and are placing a substantial 32 burden on economies and ecosystems worldwide. Of the emerging fungal diseases, 33 chytridomycosis caused by the fungus Batrachochytrium dendrobatidis (hereafter Bd) is causing 34 a global amphibian extinction. The host frog does have come internal innate immunity, as well as 35 additional resistance through cutaneous microbial communities, leading to the development of 36 probiotic bacterial therapies with mixed results. Unknown is the role of fungi in the protection 37 against Bd infection, and as such, we examined the overlapping roles of bacterial and fungal 38 microbiota in pathogen defense with a combination of high-throughput sequencing and culturing 39 of symbiotic fungi from poison arrow frogs (Dendrobates sp.). Our analyses revealed that 40 abundance of cutaneous fungi contributed more to pathogen defense (~45%), than bacteria 41 (~10%) and these differed from environmental microbiota. Further, we demonstrated that a 42 fungal probiotic therapy did not induce an endocrine-immune reaction in contrast to bacterial 43 probiotics that stressed amphibian hosts and suppressed antimicrobial peptide responses, limiting 44 their long-term colonization potential. Our results suggest that probiotic strategies against 45 amphibian fungal pathogens should refocus on host-associated and environmental fungi such as 46 Penicillium and member of the families Chaetomiaceae and Lasiosphaeriaceae. 47