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Science: Toxic germs on its skin make this newt deadly

 The skin bacteria make a paralytic toxin also found in pufferfish

Bacteria on the skin of some rough-skinned newts may make those newts deadly to predators. The microbes make a paralyzing poison called tetrodotoxin.

Some newts living in the western United States are poisonous. Bacteria living on their skin make a powerful paralyzing chemical. It’s called tetrodotoxin (Teh-TROH-doh-TOX-in). These rough-skinned newts appear to borrow the poison to avoid becoming some snake’s lunch.
The toxin, known by the initials TTX, stops nerve cells from sending signals that tell muscles to move. When animals swallow the poison in low doses, it can cause a tingling or numbness. Higher amounts cause paralysis and death. Some newts host enough TTX to kill several people.

This poison is not unique to the newts. Pufferfish have it. So does the blue-ringed octopus, some crabs and starfish, not to mention certain flatworms, frogs and toads. Marine animals, such as the pufferfish don’t make the TTX. They get it from bacteria living in their tissues or by eating toxic prey. 

It had been unclear how rough-skinned newts (Taricha granulosa) got their TTX. Indeed, not all members of the species have it. The amphibians don’t appear to pick up the lethal chemical through their diet. And a 2004 study had hinted that the newts didn’t host TTX-making bacteria on their skin. All of this suggested the newts might make TTX.

But TTX is not easy to make, notes Patric Vaelli. He’s a molecular biologist at Harvard University in Cambridge, Mass. It seemed unlikely that newts would make this poison when no other known animal can.

Vaelli led the new study while he was at Michigan State University in East Lansing. He and his team decided to double check for toxin-making bacteria on the newts’ skin. In the lab, they grew up colonies of bacteria collected from the newts’ skin. Then they screened these germs for TTX.

The researchers found four types of bacteria that make TTX. One group was Pseudomonas (Su-duh-MOH-nus). Other bacteria from this group make TTX in pufferfish, the blue-ringed octopus and sea snails. It turned out that poisonous newts had more Pseudomonas on their skin than did rough-skinned newts from Idaho that aren’t toxic.

The data offered the first known instance of TTX-making bacteria on a land animal. Vaelli’s team reported its results April 7 in eLife.
But there may be more to the story

The new data do not necessarily “shut the book” on the idea that newts can produce TTX, says Charles Hanifin. He’s a biologist at Utah State University in Logan. Newts have some forms of the toxin that scientists have yet to see in bacteria. Researchers also still don’t know how bacteria make TTX. That makes it harder to conclude precisely where the newts’ poison comes from, Hanifin argues.

But the finding does add a new player to an evolutionary arms race that pits newts against garter snakes (Thamnophis sirtalis). Some snakes living in the same regions as toxic newts have developed resistance to TTX. These snakes can then feast on TTX-laden newts.

It’s possible that Pseudomonas bacteria have become more abundant on newts over time. As levels of the bacteria have risen, the animals would have turned more toxic. Then, Vaelli says, the pressure would be back on snakes to evolve greater resistance to the toxin.

Power Words 

Amphibians: A group of animals that includes frogs, salamanders and caecilians. Amphibians have backbones and can breathe through their skin. Unlike reptiles, birds and mammals, unborn or unhatched amphibians do not develop in a special protective sac called an amniotic sac.

Bacteria: (singular: bacterium) Single-celled organisms. They dwell nearly everywhere on Earth, from the bottom of the sea to inside other living organisms (such as plants and animals). Bacteria are one of the three domains of life on Earth.

Biologist: A scientist involved in the study of living things.

Cell: The smallest structural and functional unit of an organism. Typically too small to see with the unaided eye, it consists of a watery fluid surrounded by a membrane or wall.

Chemical: A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O.

Data: Facts and/or statistics collected together for analysis but not necessarily organized in a way that gives them meaning.

Diet: The foods and liquids ingested by an animal to provide the nutrition it needs to grow and maintain health. (verb) To adopt a specific food-intake plan for the purpose of controlling body weight.

Evolve: (adj. evolutionary) To change gradually over generations, or a long period of time. In living organisms, such an evolution usually involves random changes to genes that will then be passed along to an individual’s offspring. These can lead to new traits, such as altered coloration, new susceptibility to disease or protection from it, or different shaped features (such as legs, antennae, toes or internal organs).

Germ: Any one-celled microorganism, such as a bacterium or fungal species, or a virus particle. Some germs cause disease. Others can promote the health of more complex organisms, including birds and mammals. The health effects of most germs, however, remain unknown.

Host: (in biology and medicine) The organism (or environment) in which some other thing resides. Humans may be a temporary host for food-poisoning germs or other infective agents.

Marine: Having to do with the ocean world or environment.

Molecule: An electrically neutral group of atoms that represents the smallest possible amount of a chemical compound. Molecules can be made of single types of atoms or of different types. For example, the oxygen in the air is made of two oxygen atoms (O2), but water is made of two hydrogen atoms and one oxygen atom (H2O).

Muscle: A type of tissue used to produce movement by contracting its cells, known as muscle fibers. Muscle is rich in protein, which is why predatory species seek prey containing lots of this tissue.

Nerve: A long, delicate fiber that transmits signals across the body of an animal. An animal’s backbone contains many nerves, some of which control the movement of its legs or fins, and some of which convey sensations such as hot, cold or pain.

Octopus: Sea mollusks with a soft, sac-shaped body and eight tentacles. Two rows of suckers along each tentacle give the animal an ability to grasp and hold onto things. Cousins of the squids, these animals have a sharp beak-like mouth and good vision.

Paralysis: The inability to willfully move muscles in one or more parts of the body. In some cases, nerves that carry the signal to move may have been severed or damaged. In other cases, the brain may be the source of the problem: It may fail to understand or act on a nerve’s signal to move.

Pressure: Force applied uniformly over a surface, measured as force per unit of area.

Prey: (n.) Animal species eaten by others. (v.) To attack and eat another species.

Resistance: (as in drug resistance) The reduction in the effectiveness of a drug to cure a disease, usually a microbial infection. (as in disease resistance) The ability of an organism to fight off disease.

Sea: An ocean (or region that is part of an ocean). Unlike lakes and streams, seawater — or ocean water — is salty.

Species: A group of similar organisms capable of producing offspring that can survive and reproduce.

Starfish: A type of sea creature that is shaped like a star. Starfish, also known as sea stars, are not true fish. They are related to sand dollars, sea urchins and sea cucumbers.

Tissue: Made of cells, it is any of the distinct types of materials that make up animals, plants or fungi. Cells within a tissue work as a unit to perform a particular function in living organisms. Different organs of the human body, for instance, often are made from many different types of tissues.

Toxic: Poisonous or able to harm or kill cells, tissues or whole organisms. The measure of risk posed by such a poison is its toxicity.

Toxin: A poison produced by living organisms, such as germs, bees, spiders, poison ivy and snakes.

Unique: Something that is unlike anything else; the only one of its kind.


Journal:​ ​​ P. Vaelli et al. The skin microbiome facilitates adaptive tetrodotoxin production in poisonous newts. eLife. Published online April 7, 2020. doi: 10.7554/eLife.53898.

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