Amphibian populations all over the world are experiencing declines due to the fungal pathogen Batrachochytrium dendrobatidis, or “Bd.” Bd is transmitted through water, often during the breeding season. Bd is a deadly bacterial invader, which attacks dead skin cells that are characteristic of keratinized tissues. Keratinized tissue is found in the mouths of tadpoles and on the skin of adult frogs. Humans also have keratinized tissues in our digestive tract and gums, and keratin makes up the hair and feathers of many species, but Bd is a pathogen specific to amphibians.

Through the pet trade and translocation of infected individuals, Bd has spread to habitats all over the world. International legislation put in place by the World Organisation for Animal Health now lists Bd as a notable disease in need of regulation. The presence of Bd in the environment is problematic because it is highly infectious. Amphibians breathe and absorb nutrients through their keratinized skin, so by invading these cells Bd kills amphibians by causing suffocation or malnourishment. More details about Bd and how it affects amphibians can be found on the Amphibian Ark website, one of several organizations fighting to preserve amphibian populations and biodiversity.

As explained by the Honduras Amphibian Rescue and Conservation Center, or HARCC, amphibian biodiversity is essential in maintaining clean drinking water, controlling the spread of human diseases, and sustaining ecosystem food webs. HARCC is featured in this National Geographic video, which further explains the importance of conserving amphibians and the projects being carried out at HARCC in order to do so.

One method used to combat individual infection and the spread of Bd is to collect tadpoles and raise them in quarantine until healthy adults can be released back into the wild. The goal of this process is to protect the frogs during their most vulnerable time, metamorphosis, when tadpoles transform into their adult body form. Professor Matthew Fisher, from Imperial University in London explains more about that process in this video.

This 2018 study published in Frontiers in Microbiology could hold the solution to this dilemma. Researchers from James Cook University in Australia quantified the skin microbiota of frogs in relation to Bd infection rate and found that probiotics may reduce infection levels.

At an upland (high elevation) and lowland (low elevation) site at each of the Wooroonooran National Park and Murray Upper National Park, researchers swabbed three frog species, shown to the left, to test the abundance and diversity of microbiota on their skin as well as Bd infection presence.

Thirty-two of the 110 sampled individuals were infected with Bd, but “the prevalence of infection differed significantly between species and among sites.”

When they compared the varying infection prevalence to the bacteria cultured, or grown, from skin swabs of each frog, they found a correlation: “There was a significant negative relationship between the upper limit of Bd infection intensity and the number of total inhibitory bacteria genera on infected frogs.”

This means that the more anti-Bd bacterial types that were present on the frog’s skin, the less intense the infection with Bd, measured as the amount of Bd found on the skin by swabs. This finding suggests that a diverse skin microbiome could act as a protective layer against Bd infection. Imagine troops of bacteria like Pseudomonas and Enterobacter defending frogs from Bd-invaders, all on the microscopic level.

The importance of this study lies in that some amphibian species have more anti-Bd skin microbiota than others. The researchers found types of bacteria on these three species that not only fight Bd infection, but that are culturable, so they may be grown in labs. These cultured anti-Bd bacterial troops may then be deployed into the environments of amphibians without anti-Bd bacteria in the hopes that doing so would result in a reduction of Bd in the environment, as well as colonization of these protective bacteria on the skin of species currently lacking them. Ideally this could allow susceptible amphibians to persist against Bd presence and infection, which could slow and ultimately reverse amphibian population declines.

So, the problem is solved? Unfortunately not quite. Before anti-Bd bacteria can be deployed to fight infection in populations lacking the defense, further research must be conducted. While Bd is a lethal invader of amphibian keratinized tissue, researchers do not yet know if anti-Bd bacteria could be invaders, rather than protectors, of amphibians that have evolved without them. Adding to the attack on amphibians will only further population declines, so researchers want to ensure that the outcome will be beneficial.

Savannah Weaver is a Junior at Bucknell University working towards a B.A. in Biology and a B.A. in Environmental Science.

As a Bucknellian, Savannah has played for the Varsity Women’s Water Polo team, facilitated organic chemistry study groups, and led camping and paddling trips for Bucknell Outdoor Education and Leadership (OEL). Savannah is also a member of Chi Omega and is currently a Teaching Assistant for one of the biology core courses, Evolution and Ecology.

Savannah is a Presidential Fellow, and works with Dr. Matthew McTammany to study the habitat quality of local agricultural streams before and after restoration projects. This previous summer, Savannah stayed at Bucknell as a McKenna Environmental Intern to do similar water chemistry research on the Susquehanna River.

Savannah is looking forward to studying abroad next semester in Australia, and after graduating from Bucknell, she plans on attending graduate school. Savannah hopes to be an expert on ecology and have a career dedicated to wildlife conservation.