MCA: Integrating immune system and microbiome function during amphibian development

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Microbial organisms, such as bacteria, often live in a symbiotic relationship with animals and provide beneficial functions that support health of the host animals. For many of these bacterial and animal symbiotic relationships, we know very little about their specific biology and what kinds of beneficial functions the symbiotic partners provide. Like most vertebrate animals, amphibians have complex immune systems with innate and adaptive immune functions, however amphibians do not develop a fully capable immune system until after they metamorphose from the aquatic tadpole life stage. The investigator proposes a novel hypothesis postulating that the symbiotic skin bacteria on aquatic tadpoles provide protective defensive functions while the immune system is not yet mature. The project will test this idea using an experimental approach that will examine the immune system and bacterial symbionts of an amphibian during its development from the egg and tadpole stages through metamorphosis. The Colorado Boreal Toad will be featured in this work, and it is locally endangered in the Southern Rocky Mountains due to a fungal skin pathogen. This project will advance understanding of the ways in which Boreal Toads defend themselves against the pathogen which can be helpful for conservation of the species. The investigator is a mid-career scientist who will work with a collaborator and mentor to expand learning how to apply immunology methods to amphibian disease research. The investigator is also dedicated to service in her position to support diversity, equity and inclusion as the director of graduate studies in her unit. Host-associated microbes provide a range of beneficial and necessary functions for their host organisms, yet the processes that drive the assembly of host-associated microbial communities is a significant knowledge gap. This project will study microbiome function on the skin of amphibians in order to examine the role of symbiotic microbes in pathogen defense and how that functioning changes during amphibian development. Growing a complex immune system that is capable of targeting and ridding harmful pathogens takes significant developmental time, and most of the adaptive immune system of amphibians does not come online until after metamorphosis. This begs the question, how do larval, aquatic amphibians defend themselves against a sea of opportunistic pathogens prior to the full functioning of the immune system? This project will test the idea that larval amphibians assemble a symbiotic microbial community with pathogen defense as a primary function, the ‘microbial surrogate defense system hypothesis’, prior to the maturation of the immune system. The investigator proposes a time-series experiment that will track the symbiotic skin bacteria and immune function during boreal toad development and conduct three pathogen challenge trials that will occur before, during, and after metamorphosis, respectively. The project will use both culture-dependent and sequencing tools to characterize the bacterial symbionts and immunogenomic and transcriptomic tools to characterize immune function. This project represents a first-time collaboration between the PI and a research Partner who will provide expertise on amphibian immunogenetic tools as well as mentoring related to career advancement for the PI.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.