By setting up home in the guts of pufferfish or the salivary glands of blue-ringed octopuses, they are in a good position to take food from their host, while at the same time providing a valuable defensive weapon. What remains unclear is why the bacteria evolved TTX in the first place. But Mosher is quick to reject that explanation. He sent samples of his newt toxin to a lab specifically to test for antibacterial activity in the 1960s. Of course, it's possible that TTX might help bacteria fight the immunological defences of animals such as the hapless sea urchins.
Nobody knows for sure.
Peter Anderson, a comparative neurobiologist from the University of Florida, believes the most likely explanation is that TTX is just a spectacular by-product of mundane bacterial metabolism. Many Vibrio bacteriamanipulate sodium gradients across cell membranes to fuel the rotor-like flagella that allow them to scoot around. If Anderson is right, the poison's vicious effects are purely coincidental. While some animals have evolved to tum TTX's dark powers into venom or a deterrent against attackers, humans are now learning to put the poison to good use. It has a place in the neuroscientist's tool kit as a molecular probe.