Mitigating amphibian chytridiomycosis with bioaugmentation: characteristics of effective probiotics and strategies for their selection and use

Abstract

Probiotic therapy through bioaugmentation is a feasible disease mitigation strategy based on growing evidence that microbes contribute to host defences of plants and animals. Amphibians are currently threatened by the rapid global spread of the pathogen, Batrachochytrium dendrobatidis (Bd), which causes the disease chytridiomycosis. Bioaugmentation of locally occurring protective bacteria on amphibians has mitigated this disease effectively in laboratory trials and one recent field trial. Areas still na€ ıve to Bd provide an opportunity for conservationists to proactively implement probiotic strategies to prevent further amphibian declines. In areas where Bd is endemic, bioaugmentation can facilitate repatriation of susceptible amphibians currently maintained in assurance colonies. Here, we synthesise the current research in amphibian microbial ecology and bioaugmentation to identify characteristics of effective probiotics in relation to their interactions with Bd, their host, other resident microbes and the environment. To target at-risk species and amphibian communities, we develop sampling strategies and filtering protocols that result in probiotics that inhibit Bd under ecologically relevant conditions and persist on susceptible amphibians. This filtering tool can be used proactively to guide amphibian disease mitigation and can be extended to other taxa threatened by emerging infectious diseases.

Dietary Carotenoid Supplementation Enhances the Cutaneous Bacterial Communities of the Critically Endangered Southern Corroboree Frog (Pseudophryne corroboree)

“…These enhanced bacterial community attributes could act to aid amphibian immunity by leaving less niche space and/or adhesion sites available to invading pathogens, including Bd [ 9,31 ]. Additionally, pathogen colonisation may be reduced on amphibians supporting greater cutaneous bacterial abundance and richness due to the presence of competitively superior bacteria species capable of the secretion of antimicrobial compounds, known as antiBd species [ 31,32 ].…”

Inhibitory bacteria reduce fungi on early life stages of endangered Colorado boreal toads (Anaxyrus boreas)

“…Manipulations of skin microbial communities have been proposed as one possible tool, coupled with reintroductions to improve survival (Bletz et al, 2013). We highlight taxa that associate with disease at sites, however experimental work is needed to confirm associations between host-associated microbial communities and disease.…”

“…Taxonomic groups including Burkholderiales, Actinomycetales, Pseudomonadales and Sphingomonadales were prevalent Bd-inhibitory bacteria (Figure 5b) that were also negatively co-occurring with fungi in our network analysis (Figure 3b). This information suggests that probiotic approaches to disease management (Harris et al, 2009;Bletz et al, 2013) have merit and that enrichment for Bd-inhibitory bacteria may be a host strategy to boost defenses against fungal pathogens, particularly during early developmental stages. Surprisingly we did not find Bd-inhibitory bacteria to significantly differentiate by Bd presence or absence at a site or by infection intensity.…”

“…Chytridiomycosis is a leading cause of amphibian declines worldwide (Kilpatrick et al, 2010;Bletz et al, 2013). We therefore investigated the skin-associated microbial communities of boreal toads (Anaxyrus boreas; previously Bufo boreas), a Bd susceptible species.…”

Pre-emptive National Monitoring Plan for Detecting the Amphibian Chytrid Fungus in Madagascar

“…The implementation of our monitoring plan, together with the development of specific protocols aimed at mitigating chytridiomycosis in case it should arrive in Madagascar (Bletz et al 2013), and the presence of an organization that coordinates Bd-related research activities in Madagascar provide the strategic action required to rapidly respond to the challenges of a chytridiomycosis outbreak. Beside identifying the pathogen and controlling strategic sites, the collaboration between several organizations and scientific participants is an important way of developing and boosting the conservation science in Madagascar.…”