Differential Immune Responses Correlate With Chytridiomycosis Severity in Italian Crested Newts.

In the midst of the current biodiversity crisis, amphibians are severely threatened by emerging diseases such as chytridiomycosis. Characterizing the mechanisms that underlie susceptibility to this disease is fundamental to improve amphibian conservation. Using a comprehensive multi-omics approach, this study investigates the impact of an exposure to the chytrid fungus Batrachochytrium salamandrivorans (Bsal) on the gene expression of Italian crested newts (Triturus carnifex) and on the bacterial symbionts that constitute their skin microbiota. Exposure to Bsal affected multiple components of the newts' immunity, from limited structural changes in their microbiota and decreased expression of keratin-encoding genes in the skin to the upregulation of genes involved in inflammation and adaptive immunity both at the site of infection (skin) and in their primary lymphoid organ (spleen). We found that chytridiomycosis severity was positively correlated with the downregulation of basal metabolism and with the upregulation of immune responses and of tissue restructuration. Together, our results suggest that in T. carnifex, Bsal susceptibility may be linked to a reallocation of energy resources from the maintenance of basal metabolism and tissue integrity towards elevated immunity and tissue restructuration.