Ecology of Amphibian-Microbial Symbioses

Symbiotic interactions between microorganisms and animals are ubiquitous in nature. Recent studies in amphibians have identified symbiotic bacterial communities that play a relevant role protecting the host against pathogens such as Batrachochytrium dendrobatidis, Bd. Many of the bacterial symbionts of amphibians that have been isolated to date produce antifungal metabolites with the capacity to inhibit Bd in vitro and in vivo. These findings have led to the development of probiotics as a promising strategy against chytridiomycosis, the disease caused by Bd, which has caused dramatic declines and extinctions of host species worldwide. In addition to Bd, amphibians are threatened by other pathogens such as Batrachochytrium salamandrivorans (Bsal) and ranavirus. The protective role of the skin microbiota, in addition to and likely in concert with the host immune responses, may be fundamental to the survival of amphibians against emerging infectious diseases. For example, host species that are tolerant or resistant to Bd have a bacterial community structure that distinguishes them from susceptible species. Recent studies in amphibian skin bacterial communities have shown that these communities are influenced by host species, host development, environmental conditions, surrounding bacterial communities that serve as reservoirs and external biotic agents like pathogens. In addition to the bacterial component, the skin microbiome is also composed of symbiotic fungi whose role remains to be determined. Moreover amphibians harbor symbiotic microbiota within their digestive tract and there is growing evidence that these microorganisms may also play an important protective role for the host.

The explosion of molecular techniques developed during the recent years has allowed researchers to explore the factors involved in structuring the skin microbiome in amphibians, which has opened a new field with many unanswered questions: How stable are skin communities? How do these communities re-establish on the skin after a disturbance? How do hosts influence the structure and function of these communities? What are the interactions occurring within these communities? And how do skin microbiomes function to protect amphibian hosts from pathogens? 

The aim of this Research Topic is to highlight recent research on amphibian microbiomes that address relevant questions on the ecology of amphibian-microbe interactions. The publications gathered in this Research Topic will not only expand our knowledge on the role of microbial symbionts of amphibians but will reveal novel insights that direct the next set of research questions.