Try anything once?
For some reason, I’ve a real hankering for Japanese food at the moment. I’ve no idea why – perhaps it’s due to me going through some old photos from when I toured across the country visiting labs about ten years ago. In one of them, I’m standing underneath a large fibreglass puffer fish outside a restaurant (no, I’m not going to post it).
Puffer fish, in case you didn’t know, is quite the delicacy in many parts of Asia. In Japan, it’s known as fugu. I didn’t eat any, though. Why not? Well, the fish is one of the most poisonous animals in the world. It must be skilfully prepared, or it’s potentially lethal: a slight tingling of the lips, and it’s goodnight. Deaths are rare nowadays, but I didn’t want to take the risk. I try to avoid eating anything that might kill me (although I did once – and only once – eat a kebab).
The root of the problem is tetrodotoxin (TTX), a lethal neurotoxin found in many animals. It currently has no known antidote. The animals themselves are not poisonous; the TTX is probably produced by symbiotic bacteria that live within them. Indeed, if you grow a puffer fish in an enclosed water system, it contains no TTX. Release it into open water, or feed it toxic puffer fish liver, and it becomes poisonous. Numerous different TTX-producing species have been identified, including those from the Pseudomonas, Vibrio and Actinomyces.
I found a paper last week in Marine Drugs in which a group of researchers have isolated a species of bacteria not previously known to produce TTX from within the intestines of the Hong Kong marine puffer fish Takifugu niphobles. This species was identified as Raoultella terrigena, a Gram-negative, rod-shaped bacterium.
Five bacterial strains were successfully isolated from the fish’s intestines, but only one was able to produce any toxic effects. The presence of TTX was confirmed by mass spectrometry. The identity of the strain was suggested initially by comparing its membrane fatty acid profile to other species on record and confirmed by ribosomal DNA sequence comparison.
The authors of the paper stress that although a TTX-producing species of bacteria was found within a puffer fish, there is no direct proof that it’s the bacteria making the fish poisonous, although it seems likely. Given some of the odd symbioses we’ve reported on this blog, it wouldn’t surprise me. I think I’ll stick to puffer fish grown in sterile water for the time being…
Yu VC, Yu PH, Ho KC, & Lee FW (2011). Isolation and Identification of a New Tetrodotoxin-Producing Bacterial Species, Raoultella terrigena, from Hong Kong Marine Puffer Fish Takifugu niphobles. Marine drugs, 9 (11), 2384-96 PMID: 22163191