A review of the paper: Wang, J., Fan, Y., Yao, Z., (2010), Isolation of a Lysinibacillus fusiformis strain with tetrodotoxin-producing ability from puffer fish Fugu obscurus and the characterization of this strain, Toxicon, 56, 640–643
Tetradotoxin (TTX) is a neurotoxin that can cause paralysis and death in humans. It was originally thought to be exclusively found in puffer fish although now it is known to be found in a wide range of taxa, both terrestrial and marine. It has recently been discovered that TTX productivity occurs in isolated forms of bacteria. The aim of this paper was to discover whether this productivity would be found in isolated bacteria associated with puffer fish.
Six female puffer fish (Fugu obscurus) were collected from China and transported to a US lab. The ovary, liver, intestine and skin were separated and the toxicity of each organ was analysed using a bioassay. The liver was also used for bacteriological examination. Bacteria were isolated, purified and cultured, and the toxin was extracted from the cultures. The toxicities of the extracts were also determined by an assay.
It was found that different organs contain different levels of TTX: the ovaries and liver had the highest, followed by the intestine and then the skin. Six bacteria cultures were found within the liver, one of which was a TTX producer (labelled B-1). The toxin extracted from this culture was injected into mice, which showed the typical symptoms of TTX poisoning. This bacterial strain showed a 98.4% genetic homology with the bacteria Lysinibacillus fusiformis. It is supposed that if there is more than a 98% homology, the two strains are of the same species. Therefore B-1 was determined to be L. fusiformis.
The amount of TTX produced by the bacteria was very low to account for the high levels of TTX within organisms. The authors suggested that this may be due to bioaccumulation within the animal but were still unsure. However, this paper did show that a bacteria associated with puffer fish was a producer of TTX, but more work is needed to determine the mechanism behind the accumulation of the toxin within animals.
2 comments:
Hey I did some research on this in second year because I found it really interesting. There are a couple of papers where the studies have shown Vibrio fischeri to be responsible for TTX production in the xanthid crab and Vibrio alginolyticus to be responsible for TTX production in the puffer fish Fugu vernicularis and the starfish Astropecten polyacanthus. Another theory was put forward by Noguchi who didn’t believe that a sufficient amount of TTX could be produced by bacteria (like your authors) and he suggested that it was accumulated throughout the food chain as the toxin is present in a wide number of species (marine and terrestrial) and that it would be highly unlikely that evolution would have led to the diverse number of species producing the same toxin. I think that this sounds like quite a good theory and I guess a way to test it would be to see if young puffer fish contain the same toxin and whether it is present in high or low concentrations. Did the authors mention anything about that in your paper? I guess it could also be possible that the bacteria produce TTX due to their exposure to the toxin or as a resistance mechanism which has allowed them to survive in its presence.
Here are a couple of the papers I mentioned if you wanted to have a look at them:
Noguchi T, Arakawa O. Tetrodotoxin- Distribution and accumulation in aquatic organisms, and cases of human intoxication, Marine Drugs. 2008; 6: 220-242.
Noguchi T, Arakawa O, and Takatani T. Toxicity of Pufferfish Takifugu rubripes cultured in netcages at sea or aquaria on land. Comparative biochemistry and physiology part D: genomics and proteomics. 2006; 1: 153-157.
There are some really interesting theories on this topic but I think this might be the most plausible! They didnt say anything about the young, only the few adult females that they sampled. I think there must be a way within the animal that these toxins are accumulated or focused to make the TTX as venemous as it is. Like you said I can't imagine that that diversity of animals happened to have evolved to produce the same toxin! Thanks for the reccomendations!
Natasha
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