The solution to amphibian decline could be skin deep

Almost half of all amphibian species are currently at risk of extinction. One cause of these huge population declines is the fungal pathogen Batrachochytrium dendrobatidis (Bd). When Bd infection occurs in large numbers it leads to the disease chytridiomycosis. During infection, the skin becomes thickened preventing the normal transfer of water and salts through the skin and leading to death. Chytridiomycosis causes mass mortality in populations, but some species have shown resistantance to the disease. These resistant species are still of concern as they are carriers of the disease and can spread it to new populations. Some skin bacteria prevent the growth of fungal pathogens in amphibians and could be used as a way of combatting this devastating disease.

A recent study by scientists at Virginia Tech has shown that it is possible to culture some of the dominant bacterial communities in amphibians. The study included 64 individuals across 4 species; Bullfrogs (Lithobates catesbeianus), eastern newts (Notophthalmus viridescens), spring peepers (Pseudacris crucifer), and American toads (Anaxyrus americanus). Each individual was cleaned to remove debris and swabs used to collect the skin bacteria.

Two methods were used to identify microbial communities. MiSeq Illumina sequencing provided a more complete assessment of microbial communities without the need for culturing bacteria. The second method cultured bacteria for 14 days before populations were distinguished by physical features and then identified using DNA sequencing. Whilst providing similar results to the initial method, this technique can also provide an understanding of the function of bacterial communities and be useful in the development of probiotics.

Bacterial communities varied between species, but Proteobacteria were found to be the most abundant. It was these dominant bacteria which were able to be successfully cultured and at a species level 2.81 – 7.47% of bacteria was culturable. To increase the consistency and diversity of the bacterial culture requires some refining of methodology, but the study highlights the value of bacterial culture in understanding bacterial diversity and function.  In the future it might be possible to utilise these bacteria against Bd fungus.

Reference:

Walke JB, Becker MH, Hughey MC, Swartwout MC, Jensen RV, Belden LK. 2015. Most of the dominant members of amphibian skin bacterial communities can be readily cultured. Appl Environ Microbiol 81:6589–6600. doi:10.1128/AEM.01486-15.

Featured Image: Testing frogs for chytrid fungus infection.Veronica Olsen, CSIRO.

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Becky Watson

An evolutionary ecologist with a passion for science and a particular interest in wild physiology. Rebecca studied undergraduate Zoology with honours at the University of Glasgow, including a masters year (M.Sci). Currently a PhD student at the University of Edinburgh her research focuses on understanding the causes and consequences of immune variation in the wild.
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