Abstract
Beneficial cutaneous bacteria on amphibians can protect against the lethal disease chytridiomycosis, which has devastated many amphibian species and is caused by the fungus Batrachochytrium dendrobatidis. We describe the diversity of bacteria on red-backed salamanders (Plethodon cinereus) in the wild and the stability of these communities through time in captivity using culture-independent Illumina 16S rRNA gene sequencing. After field sampling, salamanders were housed with soil from the field or sterile media. The captive conditions led to different trajectories of bacterial communities. Eight OTUs present on >90% of salamanders in the field, through time, and in both treatments were defined as the core community, suggesting that some bacteria are closely associated with the host and are independent of an environmental reservoir. One of these taxa, a Pseudomonas sp., was previously cultured from amphibians and found to be antifungal. As all host-associated bacteria were found in the soil reservoir, environmental microbes strongly influence host–microbial diversity and likely regulate the core community. Using PICRUSt, an exploratory bioinformatics tool to predict gene functions, we found that core skin bacteria provided similar gene functions to the entire community. We suggest that future experiments focus on testing whether core bacteria on salamander skin contribute to the observed resistance to chytridiomycosis in this species even under hygenic captive conditions. For disease-susceptible hosts, providing an environmental reservoir with defensive bacteria in captive-rearing programs may improve outcomes by increasing bacterial diversity on threatened amphibians or increasing the likelihood that defensive bacteria are available for colonization.
Highlights
Host-associated bacterial communities affect health in many species, including humans (Fierer et al, 2012), corals (Rosenberg et al, 2007), insects (Dillon et al, 2005) and amphibians (Harris et al, 2009a,b)
The cutaneous microbial community of amphibians provides a defensive function against pathogens, including the fungus Batrachochytrium dendrobatidis (Bd) (Woodhams et al, 2007; Becker and Harris, 2010)
Host microbiota performs a number of important functions for their hosts, such as disease resistance (Dillon et al, 2005; Rosenberg et al, 2007; Harris et al, 2009a,b; Becker and Harris, 2010), metabolism, vitamin production, development and activity of the immune system and behavior (Turnbaugh et al, 2007)
Summary
Host-associated bacterial communities affect health in many species, including humans (Fierer et al, 2012), corals (Rosenberg et al, 2007), insects (Dillon et al, 2005) and amphibians (Harris et al, 2009a,b). We experimentally examined the stability and diversity of red-backed salamander (Plethodon cinereus) microbiota through time under different environmental conditions. Understanding the importance of environmental environment for each salamander was sampled reservoirs for the hosts’ microbial community by being swabbed with 10 strokes back and forth. Reservoirs, which might strongly affect microbial Salamanders were randomly assigned to one of two structure, diversity and function of the skin treatments to test the hypothesis that the type of microbiota. We tested the hypothesis that a natural soil placement in the salamander containers, and initial bacterial reservoir was required to maintain the soil samples were taken in triplicate for bacterial stability and diversity of bacterial communities on community identification.
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