Bacteria on Poison Dart Frog Skin May Use Toxins as Food

by SHINE

Toxic chemicals found on the skin of poison dart frogs may serve as a feast for certain bacteria, scientists have discovered. These potent toxins, which act as a defense mechanism against predators, could also help shape the microbiome on the frogs’ skin.

In a study published on December 4 in Current Biology, researchers found that the alkaloid toxins secreted by poison dart frogs encourage a more diverse range of microbial species to thrive on their skin. Intriguingly, some of these microbes appear to be consuming the toxins as a source of nourishment.

Poison dart frogs (Dendrobatidae) gather toxic alkaloids from the insects and arthropods in their diet, which they accumulate in their skin. These alkaloids are poisonous to potential predators and serve as a natural defense mechanism. The chemicals are also antimicrobial, which led biologist Stephanie Caty to investigate how they might influence the composition of bacteria and fungi living on the frogs’ skin.

While a graduate student at Stanford University, Caty and her team collected bacterial and fungal samples from the skin of 11 species of poison dart frogs in Ecuador. They analyzed the genetic material of the samples to identify the microbes present and measured the levels of alkaloids on the frogs’ skin. The frogs were categorized into three groups: high, medium, and low alkaloid concentrations.

The study revealed that frogs with higher concentrations of toxic alkaloids harbored a greater diversity of bacterial and fungal species. Further experiments showed that when one species of lab-reared poison dart frogs was fed the alkaloid decahydroquinoline (DHQ), the microbial community on their skin became more diverse.

These findings suggest that the hostile, toxin-laden environment of the frogs’ skin creates a unique ecological niche that certain microbes are able to exploit. Some bacteria, in particular, appear to be thriving by feeding on the alkaloids.

To investigate this further, Caty and her colleagues introduced ammonium and DHQ to bacterial colonies modified with heavy nitrogen and carbon isotopes. By tracking where the isotopes went, they discovered that some bacteria incorporated the carbon atoms from DHQ into their cells. This suggests that the bacteria were using the alkaloids to build new cellular material.

This discovery is not entirely unprecedented. Some bacteria are known to metabolize toxic compounds like caffeine, and certain microbes in the guts of desert woodrats break down toxins from creosote plants, providing a detoxifying benefit to their hosts.

The new research adds another layer to our understanding of how poison dart frog alkaloids interact with the environment. According to Andrés Brunetti, a chemical ecologist at the Max Planck Institute for Chemical Ecology in Jena, Germany, previous studies have primarily focused on the role of alkaloids in deterring predators. However, this new research introduces the microbes as another key player in the ecosystem, highlighting the complexity of the interactions at play.

Caty believes that these findings could lead to further research on how the frogs’ microbiomes contribute to their resistance to infections. Poison dart frogs, for example, seem to be less susceptible to the chytrid fungus, a deadly disease affecting amphibians worldwide. The combination of their toxic skin and unique microbial communities might offer them some form of protection.

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