Cutaneous bacteria, but not peptides, are associated with chytridiomycosis resistance in Peruvian marsupial frogs.

Amphibians are a highly threatened vertebrate group, and populations of these animals have declined drastically. An important global threat to amphibians is the pathogenic fungus Batrachochytrium dendrobatidis (Bd), which causes the disease chytridiomycosis. However, not all species develop chytridiomycosis when exposed to Bd. We compared susceptibility to disease in two species of marsupial frogs and found that Gastrotheca nebulanastes is susceptible, whereas its congeneric G. excubitor is resistant. Since Bd is a skin pathogen, it is possible that cutaneous defenses like symbiotic bacteria and antimicrobial peptides protect the resistant species. We tested this hypothesis by comparing the anti-Bd abilities of cutaneous defenses between the two Gastrotheca species. Cultivable bacteria and peptides were isolated from the skin and tested for their abilities to inhibit Bd with in vitro co-culture assays. Twenty-six bacteria were identified by sequencing their 16S rRNA gene and 19 peptides were profiled by MALDI TOF mass spectrometry. We found that bacteria, but not peptides, differed between the two species in their ability to inhibit Bd growth. The resistant G. excubitor harbored more isolates of cultivable anti-Bd bacteria both in number and proportion (6/15 vs. 1/11). Also, the one anti-Bd isolate from G. nebulanastes demonstrated the weakest ability to inhibit Bd growth. Our results highlight the importance of anti-Bd skin bacteria in providing frog species with protection from Bd and can inform mitigation strategies for other wildlife diseases. [ABSTRACT FROM AUTHOR]