The poisonous rough-skinned newt Taricha granulosa, which can kill an adult human, turns out not to be poisonous itself. This salamander from North America carries a collection of bacteria on its skin, which produce the poison for it. Scientists from Michigan State University, University of Idaho, and others, published their findings on April 7, 2020 in the scientific journal eLife.
The salamander is not sensitive to the poison of the bacteria. It has specific mutations in its DNA, causing small changes in the cells, scientists discovered. That way, the poison cannot bind in the cell and cannot cause harm to the salamander. These mutations are not only efficient in salamanders, but also in other animals. In the lab, the researchers copied the genetic adaptations of the salamander into mouse cells. These became insensitive to the poison as well.
Unfortunately for the salamander, some snakes have also discovered this trick. For many years, a chess game has been going on between the salamander and this predator: snakes eat the salamanders, the salamanders defend themselves with a coat of poisonous bacteria, and then snakes strike back by becoming insensitive to the poison. Now it’s the salamander’s move. The poison-producing bacteria on its skin produce more poison and become even more toxic. Such a chess match between prey and predator is called co-evolution.
With that, the researchers stumbled onto a new conundrum. During the chess match of co-evolution, the opponents take turns making changes in their genetic material, which they then pass on to their offspring. In the case of the salamander, the poison production is not stored in its own DNA, but in that of the bacteria. How do they keep playing the chess game from generation to generation? Although there is no clear answer yet, the researchers have a suspicion: “The salamander’s eggs also contain poison, so the females may transfer the poison-producing bacteria to their young via the eggs”.
Were it bacteria all along?
The salamander Taricha granulosa is not the only animal carrying the poison tetrodotoxin. The poison is the same as the one found in the well-known deadly puffer fish, a popular but dangerous delicacy in Japan. Some octopuses, crabs and starfish also contain the substance. Previously, scientists studied some of these sea creatures and discovered that poisonous bacteria were the source of the toxin.
Therefore, researchers suspected that salamanders too carry poison-producing bacteria on their skin. To test their idea, they scraped the microorganisms from the salamander’s skin using a cotton swab. They grew them in a cocktail of nutrients and then measured whether the poison was present in each of the bacteria species. That was the case for four of them. Now that researchers have proven that not only sea animals, but also land and freshwater animals carry these toxic bacteria on their skin, it could mean that none of the animals produce the poison tetrodotoxin themselves, but bacteria do.
The poison tetrodotoxin affects a specific part of the cells in the body of humans and animals: sodium pumps. These pumps are the channel for the electrical signals from, for example, the brain to the muscles. The poison binds to these pumps and thereby blocks the passage, so cells can no longer transmit signals. That leads to paralysis of muscles, including those of the respiratory tract, making it impossible to breath. All this can be caused by small bacteria, invisible to the naked eye. This way they protect the animals on which live, like the rough-skinned newt.
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