Here is a summary of the project:

    A central goal of population and community ecology is to understand factors that lead to the emergence of infectious diseases in wildlife.  Our research has identified individual and population-level variation in susceptibility to a cutaneous fungal infection in three species of amphibians.  We are investigating the role of beneficial cutaneous bacteria in generating this variation and in protecting individuals from a lethal fungal pathogen.

    Amphibian skin is attacked by a fungal pathogen, Batrachochytrium dendrobatidis, which is a chytrid fungus.  This disease has caused widespread population declines and apparent extinctions in areas of the world, such as Australia and the Americas.  Our hypothesis is that study of the ecological context of emerging infectious diseases, such as chytridiomycosis, is crucial in understanding and eventually controlling the disease.  The ecological context is the interaction of the dispersing zoospore of B. dendrobatidis and the resident anti-chytrid bacterial flora on amphibian skin.

    Our research has shown that the skin of healthy amphibians (salamander Plethodon cinereus) is populated by resident bacteria and that a number of cutaneous bacterial species have anti-chytrid properties.  The dispersing zoospores of the pathogen will likely interact with the amphibian’s cutaneous bacterial microbiota and may be inhibited by it.  In the laboratory, our research has shown that a “probiotic” application of beneficial bacteria followed by exposure to the chytrid pathogen can speed clearance time of the chytrid infection in P. cinereus.  From field data, a comparison was made of the skin  microbiota of populations of the frog Rana muscosa that are coexisting with the pathogen with those that decline once the pathogen arrives.  A significantly higher proportion of individuals in the persisting population had at least one species of anti-chytrid bacteria on the skin.

    We are testing the efficacy of the application of anti-chytrid bacteria to the skin of two anuran species that are negatively affected by B. dendrobatidis.  Our hypothesis is that application of bacteria will have a protective effect against the negative effects of B. dendrobatidis.  We are also studying:  (1)  the effects of stress on individual amphibian’s cutaneous microbiota and susceptibility to chytridiomycosis, (2) the role of horizontal and vertical transmission of skin bacteria, (3) antibiotics produced by skin bacteria.  The potential discovery of antifungal molecules opens the door to a novel chemotherapeutic that could be applicable not only to amphibian conservation but to human medicine.

    I am collaborating with Dr. Lisa Belden at Virginia Tetch on the role of beneficial microbes in preventing disease.


References:  (* = student coauthor)

Banning*, J. L., A. L. Weddle*, G. W. Wahl III*, M. A. Simon, A. Lauer, R. L. Walters*, and R. N. Harris. 2008. Antifungal skin bacteria, embryonic survival, and communal nesting in four-toed salamanders, Hemidactylium scutatum. Oecologia 156:423–429

Belden, L. K., and R. N. Harris. 2007. Infectious diseases in wildlife:  the community ecology context. Frontiers in Ecology and Environment 5:533-539.

Brucker*, R. M., C. M. Baylor*, R. L. Walters*, A. Lauer, R. N. Harris, and K. P. C. Minbiole. 2008. The identification of 2,4-diacetylphloroglucinol as an antifungal metabolite produced by cutaneous bacteria of the salamander Plethodon cinereus. Journal of Chemical Ecology 34:39-43.

Harris, R. N., T. Y. James, A. Lauer, M. A. Simon, A. Patel*. 2006. The amphibian pathogen Batrachochytrium dendrobatidis is inhibited by the cutaneous bacteria of amphibian species.  EcoHealth 3:53-56.

Lauer, A., M. A. Simon, J. L. Banning*, E. André*, K. Duncan*, and R.  N. Harris.  2007. Common cutaneous bacteria from the eastern red-backed salamander can inhibit pathogenic fungi. Copeia, 2007: 630-640.

Lauer, A., M. A. Simon, J. L. Banning*, B. Lam*, and R. N. Harris. 2008. Diversity of cutaneous bacteria with antifungal activity isolated from female four-toed salamanders.  The ISME Journal 2, 145–157.

Woodhams, D. C., V. T. Vredenburg, M. J. Stice, M. A. Simon, D. Billheimer, B. Shakhtour, Y. Shyr, C. J. Briggs, L. A. Rollins-Smith, and R. N. Harris. 2007. Symbiotic bacteria contribute to innate immune defenses of the threatened mountain yellow-legged frog, Rana muscosa.  Biological Conservation, 138: 390-398.

Woodhams, D. C., L. A. Rollins-Smith, R. A. Alford, M. A. Simon & R. N. Harris. 2007. Response - Innate immune defenses of amphibian skin: antimicrobial peptides and more. Animal Conservation 10: 425–428



Below are some references to our work in science press:

BBC web page

MicrobeWorld

JMU Web Publication related to our work on beneficial cutaneous bacteria.

News article in Nature.com (need to be on campus to view)

News article in National Geographic News

News article in New Scientist






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