Associations between skin bacteria and chytrid fungal infection in Asian amphibians

Identifying the generality of defensive symbionts and microbiome structures associated with pathogen infection across multiple hosts provides insights into understanding disease susceptibility and managing disease. The fungus <i>Batrachochytrium dendrobatidis</i> (<i>Bd</i>) infects amphibian skin (the disease, chytridiomycosis), causing amphibian declines worldwide except in Asia. Here, we investigated associations between amphibian skin bacterial microbiome and <i>Bd</i> infection in five Asian amphibian species and the susceptible, Australasian species <i>Litoria caerulea</i> via experiments and in the wild. We found that Asian amphibians showed resistance to <i>Bd</i> infection experimentally, with <i>Bd</i> infection causing divergence in microbiome structures in inoculated animals. Alpha diversity and relative abundances of 16 OTUs had negative effects on <i>Bd</i> load across inoculated animals. Compared with L. <i>caerulea</i>, four OTUs (Bradyrhizobium, Achromobacter, Sediminibacterium, and Rhodoplanes) with negative effects on <i>Bd</i> load were consistently enriched in experimental and wild populations of Asian amphibians. These OTUs are probably associated with reduced <i>Bd</i> loads in Asian amphibians.