Review: The Impact of Microbiome Diversity and Composition on Host Health and Susceptibility to Disease across Amphibian Life Stages

Abigail Jo MillerJamie Voyles^*

• University of Nevada, Reno, Reno, United States

Germ-free (i.e., absence of all microbes) and gnotobiotic (i.e., specific known microbial communities) study systems have classically been used to investigate the critical role the microbiome plays in the development of the host immune system. To date, most systems that have been used to experimentally manipulate the microbiome have been developed in model organisms, such as mice and pigs. However, amphibians are rapidly emerging as a valuable model for studying host–microbiome interactions and their effects on health and immunity, especially in the context of infectious disease. Amphibians are a particularly compelling system because, unlike many current systems, they include many species that do not need direct parental care during development, and they undergo a complete reorganization of their immune system during metamorphosis. Further, amphibians are of particular conservation importance as they are currently affected by the infectious disease chytridiomycosis, caused by the fungal pathogen Batrachochytrium dendrobatidis. Here, we review current research aimed at manipulating the amphibian microbiome through the use of antimicrobial treatments, with a focus on how a depletion of the microbiome diversity influences host development, immunity, and susceptibility to infectious disease. We structure our review in three parts: (1) how microbiome depletion affects chytridiomycosis disease dynamics, (2) how microbiome bioaugmentation through the use of probiotics influences susceptibility to chytridiomycosis, and (3) how microbiome depletion affects amphibian health across different life stages. Overall, research on this topic is important for the conservation of wild amphibian populations because it adds to understanding of the amphibian immune system and susceptibility to disease, both of which are important to inform management strategies and optimize potential therapeutics to aid susceptible populations.