Toxicity and distribution of tetrodotoxin-producing bacteria in puffer fish collected from the Bohai Sea of China

To investigate the relationship between the toxicity of puffer fish and the distribution of tetrodotoxin-producing bacteria in puffer fish Fugu rubripes collected from the Bohai Sea of China, bacteria were isolated from each organ (ovaries, livers, intestines and gallbladders) and screened for tetrodotoxin (TTX) production. 20 out of 36 isolated strains were found to produce TTX in vitro. In the organs of ovaries and livers whose toxicity is more potent than other organs, the number and toxicity of TTX-producing strains was greater than that of others. Most TTX-producing bacterial strains were identified as Bacillus spp. (19 strains) and Actinomycete spp. (1 strain) based on the morphological observation, physiological and biochemical characteristics and G+C content of DNA. The purified toxin was identified to be TTX by high performance liquid chromatography assay, thin-layer chromatography assay and electrospray ionization mass spectrometry analysis. Our results suggested that TTX-producing bacteria are closely related to the toxification of the puffer fish. More research is needed to elucidate the mechanism of TTX synthesis and the role of TTX in bacteria.