Composition of Micro-eukaryotes on the Skin of the Cascades Frog (Rana cascadae) and Patterns of Correlation between Skin Microbes and Batrachochytrium dendrobatidis.

Jordan G Kueneman,Valerie J Mckenzie,Sophie Weiss

doi:10.3389/fmicb.2017.02350

Jordan G Kueneman, Valerie J Mckenzie + Show 1 more

Open Access

https://doi.org/10.3389/fmicb.2017.02350

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Abstract

Global amphibian decline linked to fungal pathogens has galvanized research on applied amphibian conservation. Skin-associated bacterial communities of amphibians have been shown to mediate fungal skin infections and the development of probiotic treatments with antifungal bacteria has become an emergent area of research. While exploring the role of protective bacteria has been a primary focus for amphibian conservation, we aim to expand and study the other microbes present in amphibian skin communities including fungi and other micro-eukaryotes. Here, we characterize skin-associated bacteria and micro-eukaryotic diversity found across life stages of Cascades frog (Rana cascadae) and their associated aquatic environments using culture independent 16S and 18S rRNA marker-gene sequencing. Individuals of various life stages of Cascades frogs were sampled from a population located in the Trinity Alps in Northern California during an epidemic of the chytrid fungus, Batrachochytrium dendrobatidis. We filtered the bacterial sequences against a published database of bacteria known to inhibit B. dendrobatidis in co-culture to estimate the proportion of the skin bacterial community that is likely to provide defense against B. dendrobatidis. Tadpoles had a significantly higher proportion of B. dendrobatidis-inhibitory bacterial sequence matches relative to subadult and adult Cascades frogs. We applied a network analysis to examine patterns of correlation between bacterial taxa and B. dendrobatidis, as well as micro-eukaryotic taxa and B. dendrobatidis. Combined with the published database of bacteria known to inhibit B. dendrobatidis, we used the network analysis to identify bacteria that negatively correlated with B. dendrobatidis and thus could be good probiotic candidates in the Cascades frog system.

Highlights

Microbial symbionts of vertebrate hosts facilitate many biological processes, such as nutrient acquisition, host behavior, training of the adaptive immune system and protection against environmental pathogens (Bravo et al, 2011; Ezenwa et al, 2012; Tuddenham and Sears, 2015)
The amphibian skin microbiome has become an active area of research due to the protective role that some bacteria provide against Batrachochytrium dendrobatidis, an emerging fungal skin pathogen (Harris et al, 2009; Kueneman et al, 2016)
Both subadult and adult skin communities appeared to be dominated by pathogen B. dendrobatidis (Figure 1B)

Summary

Introduction

Microbial symbionts of vertebrate hosts facilitate many biological processes, such as nutrient acquisition, host behavior, training of the adaptive immune system and protection against environmental pathogens (Bravo et al, 2011; Ezenwa et al, 2012; Tuddenham and Sears, 2015). The amphibian skin microbiome has become an active area of research due to the protective role that some bacteria provide against Batrachochytrium dendrobatidis, an emerging fungal skin pathogen (Harris et al, 2009; Kueneman et al, 2016). This aquatic pathogen, the agent of a global pandemic, invades the keratinized epidermis of amphibians resulting in cell disruption and osmotic imbalances that can lead to death (Voyles et al, 2009). We use a parallel approach (18S rRNA marker gene sequencing) to explore micro-eukaryotic diversity alongside bacterial diversity on the skin of endangered Cascades frogs (Rana cascadae)

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