The Decline of Amphibian Populations
Amphibians are a versatile group of animals occupying both the aquatic and terrestrial ecosystems. However, 41% of all amphibians evaluated the IUCN Redlist is threatened by extinction (https://www.iucnredlist.org/). Among the many causes of population decline, we tried to provide a solution on mitigating the effects of chytridomycosis: a deadly amphibians disease.
The fungal pathogen B. dendrobatidis(Bd) is the cause of the global chytridomycosis outbreak. The disease has been transmitted along globalization and has driven multiple species, especially ones that have not coevolved with the pathogen, to the brink of extinction. An example is the Panamanian golden toads(A.zeteki) which went extinct in the wild due to the disease. It is worth noting that there is research indicating the Korean peninsula as the origin of the disease.
Violacein has shown to be effective agianst Bd. It is also a compound produced by J.lividium, which is a microbe naturally found on the skin of certain amphibians. There has been attempts to apply J.lividium to confer protection against Bd, but this approach has limited applicability, since the approach was shown to be not effective on certain species including A.zeteki. We thought by harnessing synthetic biology, we could create microbes that would be more generalizable in probiotic approaches.
Though violacein is an effective anti-Bd agent, it must be produced in an regulated manner since its anti-fungal activity is not limited to Bd. Therefore we designed constructs that could increase specificity. For better attachment and reduced falloff, we created mucus binding domains that could be displayed on the surface of microbes. For increased specificity, we created light switches and chitin detecting systems which feed inputs to the split violacein operon to achieve AND gate behavior. For better safety, quorum sensing-based kill switches were designed to kill cells that detach from the mucosal layer of amphibians.