Don’t scratch at that, it’ll only make it worse

May 24, 2006

Zippy the Pinhead periodically goes into a trance, repeating a polysyllabic three-word mantra over and over. Once in a while I stumble across a phrase in my science reading with just the right hypnotic quality to send Zippy to Zen heaven. A couple of months back, just before I began this blog, it was “nonsense mediated decay”. I may have to post about that sometime, but for today’s lesson our mantra is “giant gutless tubeworms.”

From the moment hydrothermal vents were discovered — deep ocean trench communities of organisms which get their energy not from sunlight, but rather from geothermal temperature gradients where tectonic plates meet — these guys have been media stars. As the name indicates, they are gutless wonders. They start as free-swimming larva with normal digestive systems, but they soon settle down to a sedentary life. Taking Saint Paul’s advice to extremes, they then put away childish things, including the gut, the mouth and the anus, and set about the serious adult business of putting on mass. They can grow up to eight feet long.

They get all their nutrition from symbiotic bacteria. They don’t inherit the bugs from their parents; they harbor no colonies in their free-swimming youth. What’s new this week, as reported in Nature, is the way they take on their microscopic boarders, which dwell in a specialized organ called the trophosome.

It had been thought that when it attached to the vent floor, the larva simply swallowed some of the proper bacteria, which then, by some mechanism yet to be determined, defended themselves against being digested. Not so. It turns out they are still bacteria-free when their mouths close over. Instead, the bacteria invade through their skin, and migrate to a region which then differentiates into a trophosome. While this is going on, the cells of the skin and intervening muscle go through a massive die-off, just as if they were succumbing to a nasty infection. Once the colony is ensconced, the die-off stops. The process presents a lovely example of a relationship somewhere between infectious disease and comfortably established symbiosis.

No matter how weird the life style, some organism somewhere is living it.

Giant gutless tubeworms, giant gutless tubeworms, giant gutless tubeworms. Go ahead, try it. No one can say it just once.


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