No evidence for an endosymbiotic bacterial origin of tetrodotoxin in the newt Taricha granulosa

Tetrodotoxin (TTX) is a potent neurotoxin which is known to occur in numerous taxa, including newts. The origin of TTX is unknown, but production by symbiotic bacteria is suspected for some groups. Using PCR primers that specifically amplify 16S rRNA genes of bacteria, we examined tissues from rough-skin newts, Taricha granulosa, for the presence of bacteria which may produce TTX. No amplification of bacterial DNA was seen in samples taken from skin, liver, gonads or oviposited eggs-tissues known to contain TTX. Amplification of bacterial DNA was seen only in samples taken from newt intestines, a tissue with low concentrations of TTX. These results indicate that symbiotic bacteria are unlikely to be the source of TTX in newts.