The skin microbiome facilitates adaptive tetrodotoxin production in poisonous newts.

Rough-skinned newts ( Taricha granulosa ) use tetrodotoxin (TTX) to block voltage-gated sodium (Na _v ) channels as a chemical defense against predation. Interestingly, newts exhibit extreme population-level variation in toxicity attributed to a coevolutionary arms race with TTX-resistant predatory snakes, but the source of TTX in newts is unknown. Here, we investigated whether symbiotic bacteria isolated from toxic newts could produce TTX. We characterized the skin-associated microbiota from a toxic and non-toxic population of newts and established pure cultures of isolated bacterial symbionts from toxic newts. We then screened bacterial culture media for TTX using LC-MS/MS and identified TTX-producing bacterial strains from four genera, including Aeromonas , Pseudomonas , Shewanella , and Sphingopyxis . Additionally, we sequenced the Na _v channel gene family in toxic newts and found that newts expressed Na _v channels with modified TTX binding sites, conferring extreme physiological resistance to TTX. This study highlights the complex interactions among adaptive physiology, animal-bacterial symbiosis, and ecological context.
Competing Interests: PV, KT, JW, JF, HE No competing interests declared, LO Reviewing editor, eLife
(© 2020, Vaelli et al.)