Tetrodotoxin (TTX) is a highly lethal neurotoxin, isolated from organisms belonging to six phyla within the kingdom Animalia. It is unclear why or how TTX occurs in different phylogenetically unrelated organisms. Hypotheses have been advanced that TTX is biosynthesized by symbiotic or commensal bacteria [1], and furthermore it is possible that these bacteria may need specific inductors. The possibility that non-cultivable bacteria can have an important role in the TTX biosynthesis cannot also be ignored. In this way, “omics” tools as metagenomics and metabolomics will enable the investigation of the genome and metabolome of complex microbial consortia embedded in a holobiont [2]. In this study, we have used the metabolome and metagenomic tools to investigate the occurrence of TTX in seven different holobionts from marine and terrestrial environment, including puffer fishes and frogs, and in 250 cultures of bacteria isolated from these holobionts. The microbiome associated with four of these seven hosts were subject of metagenomics analyses. The cultivable isolates have been taxonomically characterized by sequence of pyrH gene revealing several Vibrio species. TTX was found in 3 holobiont species investigated. Cultures of several bacteria, including Vibrio communis specie, showed a similar TTX ion mass at m/z 320.1091, but a fragmentation which does not correspond to the TTX standard, indicating that bacteria do not produce TTX but a distinct metabolite. Metagenome data revealed the predominance of Proteobacteria phylum in the sample analyzed and a specific microbial signature for different organs analyzed in puffer fish, all of which contains TTX.
[1] Magarlamov, T. Y., Melnikova, D. I., & Chernyshev, A. V. (2017). Tetrodotoxin-Producing Bacteria: Detection, Distribution and Migration of the Toxin in Aquatic Systems. Toxins, 9(5), 166.
[2] Kennedy, J., Flemer, B., Jackson, S. A., Lejon, D. P., Morrissey, J. P., O’gara, F., & Dobson, A. D. (2010). Marine metagenomics: new tools for the study and exploitation of marine microbial metabolism. Marine drugs, 8(3), 608-628.