Department of Integrative Biology, Michigan State University, East Lansing, United States; BEACON Center for the Study of Evolution in Action, Michigan State University, East Lansing, United States
Kevin R Theis
BEACON Center for the Study of Evolution in Action, Michigan State University, East Lansing, United States; Department of Biochemistry, Microbiology, and Immunology, Wayne State University, Detroit, United States
Janet E Williams
BEACON Center for the Study of Evolution in Action, Michigan State University, East Lansing, United States; Department of Animal and Veterinary Science, University of Idaho, Moscow, United States; Institute for Bioinformatics and Evolutionary Studies, University of Idaho, Moscow, United States
Department of Biology, Stanford University, Stanford, United States
James A Foster
BEACON Center for the Study of Evolution in Action, Michigan State University, East Lansing, United States; Institute for Bioinformatics and Evolutionary Studies, University of Idaho, Moscow, United States; Department of Biological Sciences, University of Idaho, Moscow, United States
Department of Integrative Biology, Michigan State University, East Lansing, United States; BEACON Center for the Study of Evolution in Action, Michigan State University, East Lansing, United States
Rough-skinned newts (Taricha granulosa) use tetrodotoxin (TTX) to block voltage-gated sodium (Nav) 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 Nav channel gene family in toxic newts and found that newts expressed Nav 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.
