Why do you think the probiotic treatment was not effective?
A frog’s skin is a very unique organ. It is not like a mammal’s skin, which acts like a barrier. Frogs’ skin is much more permeable to the environment. A key component of their skin is the mucus layer, and that is full of commensal bacteria that do no harm, or symbiotic bacteria that can have beneficial effects.
There are more than 3,000 species of bacteria on frogs’ skin—and they’re all competing with each other. Part of the challenge we face is that we don’t know enough about frogs’ bacterial skin ecology to change their microbiome in such a way that would allow a different skin community to become established. The host (i.e the frog) creates the environment where the bacteria thrive, and the bacterial community really responds to the host, more than the bacteria we 'seed' it with.
What’s your takeaway from this project?
This research illustrates some of the challenges we face in manipulating microbiomes and in using synthetic biology to solve real environmental problems. Ultimately, we learned that it is difficult to manipulate a frog’s microbiome. It is also difficult to predict how a bacteria will function—will it persist, or will it become dormant in the community? Although our bacteria did well against chytrid in a test tube, once placed on a frog’s skin, the “living pharmacy” failed to protect its patient.
I’m very proud of this work. We have successfully tested two really challenging ideas that have been discussed in the amphibian community for many years. We got our answer—it just wasn’t the answer we wanted. This was a technically challenging experiment, but it was also one of the most innovative and interesting research projects that I’ve done in my time at the Smithsonian Conservation Biology Institute.
This story appears in the November 2021 issue of National Zoo News. The research was led by Dr. Matthew Becker, Dr. Robert Fleischer and Dr. Brian Gratwicke of the Smithsonian’s National Zoo and Conservation Biology Institute, and Dr. Jennifer Brophy and Dr. Christopher Voigt of the Massachusetts Institute of Technology.