Tetrodotoxin (TTX) is an extremely potent low-molecular weight non-protein neurotoxin. TTX has been isolated from many different organisms, including fish, chaetognaths, gastropod molluscs and the list goes on. The fascinating property of TTX is its appearance in many genetically unrelated animals, leading to questions of the origin of TTX. An interesting theory is that bacteria may produce the substance, rather than an innate production mechanism within the organism.
Previous studies had established a direct link between TTX (including TTX derivatives) and the presence of TTX-producing bacteria. In their 2005 paper, Zhenlong Wu et al take this further to prove that distribution and toxicity of TTX-producing bacteria in each tissue of the puffer fish F. rubripes are closely related to the toxicity of the puffer fish. They also show that toxicity is higher/more potent in the liver and ovaries than in other organs, and that this corresponds with a higher number and % of total bacteria that produce sodium channel blocking toxins in these organs.
The Bacteria strain with the highest level of toxicity, 1.6MU/g compared to 0.1 (lowest) was found in the ovaries of the puffer fish, which is known to be one of the most potent organs, along with the liver. The cultured Bacteria included Bacillus (32 strains), followed by Actiomyces spp. (3 strains), and vibrio spp. (1 strain). Among 35 bacterial strains, 20 strains (13 strains from the ovaries, 6 from livers and 1 from intestines) were found to produce sodium channel blocking toxins. The percentages of toxin-producing strains from each organ were found to be 68% for the ovaries, 55% for the livers and 25% for intestines.
These results, although somewhat simple, were the first that proved that distribution and toxicity of TTX-producing bacteria were related to toxicity in the organism.
Zhenlong Wu et al put forward several projects that would help improve understanding in the future, including elucidating the exact mechanism of the synthesis of TTX by bacteria and the role of TTX in the bacteria themselves as well as discovering whether the TTX-producing bacteria accumulate through the food chain or come from the marine environment needs more research.
In the other blog posts, several papers more recent than this have been summarised and show how the TTX field has moved forward, but is still somewhat still mysterious. I feel like this is a very simple paper but one that may have been instrumental to the beginnings of this research topic. They also suggest some important future tests.
Zhenlong Wu, Ying Yang, Liping Xie, Guoliang Xia, Jiangchun Hu, Shujin Wang, Rongqing Zhang, Toxicity and distribution of tetrodotoxin-producing bacteria in puffer fish Fugu rubripes collected from the Bohai Sea of China, Toxicon, Volume 46, Issue 4, 15 September 2005, Pages 471-476.