A lethal fungal pathogen, Batrachochytrium dendrobatidis, has caused widespread population declines and apparent extinctions of amphibian species in many areas of the world. Fortunately, numerous species of bacteria are known to produce antifungal compounds and some of these species live on the skin of amphibians. This research will investigate the role of beneficial bacteria on the skin in protecting amphibians from this lethal fungal disease. This project will develop nonlethal methods to sample antifungal compounds on amphibians that are produced by their bacterial communities, and relate these antifungal compounds to disease outcome in individuals and in populations of amphibians. This work may solve a major puzzle in amphibian ecology; why are some species unaffected by the pathogen while others are greatly negatively affected? This research advances our general understanding of the role of microbial communities on protection from disease. In particular, this research program will explore whether the specific composition of bacterial species on the skin affects how well they protect the amphibian. This project is highly interdisciplinary, including ecological sampling and experimentation, laboratory culturing of bacteria and fungi, identification of antifungal compounds with liquid chromatography-mass spectrometry, and identification of microorganisms and microbial communities with DNA sequencing techniques. The risky aspects of new methods development, combined with the potentially transformative nature of the results, makes this appropriate as an EAGER project.
Amphibians are a critical part of many ecosystems, yet many amphibian populations have declined or gone extinct due to fungal infection and others are at risk. This research will provide important information that will help in ongoing and crucial conservation efforts of frog and salamander populations. Results from this project may suggest a means to inoculate populations at risk from pathogenic fungi using beneficial antifungal bacteria. In addition, this research effort will provide training in interdisciplinary research for several undergraduates, thus preparing them for graduate and professional schools.
Emerging infectious diseases are becoming a reality for many species of plants and animals, including humans. Amphibians are faced with a lethal skin fungus, Batrachochytrium dendrobatidis (Bd), which has decimated species around the world. Once an amphibian species goes extinct, we lose the ability to study its defensive chemicals, which can be excellent models for human drugs. For example, certain amphibian skin secretions are anti-HIV. In addition, the ecosystem suffers when so many species go extinct. Nutrient cycling is negatively affected and the balance of species changes. For example, algae becomes more common, since there are fewer tadpoles, and insect abundance can increase. Probiotics are naturally occurring bacteria that can be added to amphibian skins to help them defend against Bd. What is needed is a probiotic that already occurs on their skins, but that can be boosted in number. Probiotics are the only field-tested method that has worked to mitigate the disease threat. Our research has shown one reason that probiotics can be so effective. Amphibians produce their own defensive chemicals that are called antimicrobial peptides or AMPs. The probiotic bacteria secrete metabolites that kill Bd. We found that both of these chemicals together act synergistically to kill the lethal pathogen. This is important since it means that low concentrations of AMPs and the bacterial metabolites are enough to kill Bd since these molecules work together. It also means that the amphibian can produce relatively low amounts of AMPs so that the beneficial bacterial are not killed. Thus, effective probiotics will be chosen so that they work synergistically with the amphibian hosts' own AMPs. We also discovered that amphibian antifungal bacteria can kill the fungus that causes athletes' foot. This disease is very hard to treat, however a skin probiotic holds promise for controlling the fungus.
