The title of most poisonous animal on Earth is typically given to the beautiful and deadly golden poison dart frog of Columbia—the one-inch-long frog is sometimes drenched in enough poison to kill ten grown men. But a far less exotic creature is capable of producing enough poison to kill up to 20 people: the unassuming rough-skinned newt, with its bumpy skin and fiery orange underbelly, a familiar sight in the Pacific Northwest of North America.
Some populations of this common amphibian are covered in a deadly neurotoxin—a compound called tetrodotoxin (TTX) that causes paralysis and is also found in most species of pufferfish as well as the notorious blue-ringed octopus.
Scientists have long known of the newt’s toxicity, but only in some areas are they toxic enough to surpass the golden poison frog's deadliness. That’s because the newts (Taricha granulosa) are engaged in an evolutionary arms race with one of their primary predators—the common garter snake (Thamnophis sirtalis). In some places, the snakes have developed a resistance to the newt’s poison, and in response, the newts have cranked up their poison dosage.
But scientists couldn’t figure out how the newts produced a complex neurotoxin like TTX, reports Erin Garcia de Jesus for Science News. Now, new research suggests that the toxic tango between the rough-skinned newt and its serpent predator may have a third participant: bacteria living on the newt’s skin, according to a new study published in the journal eLife.
Prior research had shown that pufferfish acquire TTX via their diet and from strains of bacteria hosted in the fish’s skin and organs, but the newts didn’t appear to eat anything toxic. Some experts thought this could mean the newts were making the toxin themselves, but TTX is a complex compound to manufacture in the body, study author Patric Vaelli, a molecular biologist at Harvard University, tells Science News.
To investigate whether the amphibians might be getting a helping hand from bacteria, Vaelli and his colleagues swabbed the skin of rough-skinned newts and grew the bacteria in the lab. When researchers screened the bacteria for TTX, they found four groups of toxin-toting bacteria.
The quartet of microbes includes the genus Pseudomonas, which also produces TTX in pufferfish, the blue-ringed octopus and sea snails. The presence of Pseudomonas bacteria was also correlated with the level of toxicity in individual newts. This is the first time researchers have identified bacteria that produce TTX on a land animal.
However, the newts may still have some unexplained tricks up their sleeves, Charles Hanifin, biologist at Utah State University, tells Science News. Some permutations of TTX found on newt skin aren’t yet known to emanate from bacteria.
What’s more, nobody knows how bacteria manufacture TTX in the first place, adds Hanifin,so it's still possible that the newts may potentially be making some of the potent toxin themselves.