Abstract
Global amphibian declines and extinction events are occurring at an unprecedented rate. While several factors are responsible for declines and extinction, the fungal pathogen Batrachochytrium dendrobatidis (Bd) has been cited as a major constituent in these events. While the effects of this chytrid fungus have been shown to cause broad scale population declines and extinctions, certain individuals and relict populations have shown resistance. This resistance has been attributed in part to the cutaneous bacterial microbiome. Here, we present the first study characterizing anti-Bd bacterial isolates from amphibian populations in Costa Rica, including the characterization of two strains of Serratia marcescens presenting strong anti-Bd activity. Transcriptome sequencing was utilized for delineation of shifts in gene expression of the two previously uncharacterized strains of S. marcescens grown in three different treatments comprising Bd, heat-killed Bd, and a no Bd control. These results revealed up- and down-regulation of key genes associated with different metabolic and regulatory pathways. This information will be valuable in continued efforts to develop a bacterial-based approach for amphibian protection as well as providing direction for continued mechanistic inquiries of the bacterial anti-Bd response.
Highlights
The role of the bacterial microbiome in conferring disease resistance has been the subject of intensive study in a number of disease systems
This area has critical importance in elucidating the mechanisms of disease dynamics in the context of important host relationships with bacteria. Inquiries into such systems is an important frontier in many taxa undergoing biodiversity loss. Examples include diseases such as white-nose syndrome caused by Pseudogymnoascus destructans in bats (Hoyt et al, 2015) and chytridiomycosis caused by Batrachochytrium dendrobatidis and Batrachochytrium salamandrivorans in amphibians (Longcore et al, 1999; Martel et al, 2013)
Amphibian species A. annae, Agalychnis lemur, C. bransfordii, and Oophaga pumilio had the greatest number of anti-Batrachochytrium dendrobatidis (Bd) bacterial isolates (Supplementary Table 3)
Summary
The role of the bacterial microbiome in conferring disease resistance has been the subject of intensive study in a number of disease systems. This area has critical importance in elucidating the mechanisms of disease dynamics in the context of important host relationships with bacteria. Inquiries into such systems is an important frontier in many taxa undergoing biodiversity loss. While previous work has examined bacterial gene expression in response to disease in humans (Duran-Pinedo et al, 2014), this is generally lacking in many of the other important disease systems of animals where conservation priorities are a concern
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