Skin bacteria provide early protection for newly metamorphosed southern leopard frogs (Rana sphenocephala) against the frog-killing fungus, Batrachochytrium dendrobatidis

Abstract

An important concern for conservation biologists is the continuing loss of global biodiversity. This is especially true for amphibians, which are disappearing at an alarming rate. The emerging fungal pathogen, Batrachochytrium dendrobatidis (Bd), causes the skin disease chytridiomycosis and is a major contributor to amphibian population declines. Recent studies suggest that symbiotic skin bacteria provide some protection against Bd. Possible mitigation strategies include skin microbiome manipulation and bioaugmentation with potentially beneficial bacteria. Such approaches may employ a method to reduce resident bacteria on the skin to allow for new colonization. Using the southern leopard frog, Rana (Lithobates) sphenocephala, we show here that the skin of this species harbors a rich array of culturable bacterial species that inhibit Bd growth in vitro. Use of a potent antibiotic cocktail dramatically reduced culturable skin bacteria within 48. h. Reduction of bacteria on post-metamorphic juvenile skin using this antibiotic cocktail resulted in an increased Bd skin burden within two weeks of Bd exposure and a higher Bd burden in those frogs that died. However, efforts to maintain a normal bacterial skin community using a semi-natural mesocosm-derived source of microbes failed to provide long term protection of these vulnerable frogs. Regardless of presence or absence of mesocosm-derived bacteria, Bd loads decreased over time in surviving frogs, suggesting the development of an adaptive immune defense. In this species, development of an antimicrobial peptide defense is delayed, and thus, the microbial community and adaptive immune defenses may provide protection at this critical period of development.

Publication Title

Biological Conservation

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