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Thursday, June 20, 2013

How hot is too hot?

What’s the hottest environment in which living organisms can thrive? It depends on the organism. There are Archae (single-celled prokaryotes that used to be classified as bacteria) that have been found thriving in 122oC. Remember, that’s much hotter than the boiling point of water, and presumably of the insides of the Archae. 

Multicellular organisms can’t take that amount of heat. One of the most thermophilic (heat-loving) metazoan organisms ever discovered is the Pompeii worm (Alvinella pompejana, shown above). These are a type of bristle worm that happens to live next to hydrothermal vents on the ocean floor. Although they are known to live at temperatures of 50oC (that’s 122oF for my fellow Americans), some reports suggest that they can tolerate far hotter temperatures, even up to 100oC. 

The best way to test these assertions would be to systematically vary the temperature within a controlled setting. Unfortunately, it has been impossible to bring living Pompeii worms up from the depths of the ocean into the laboratory. Until now.

French researchers, led by Juliette Ravaux of UniversitĂ© Pierre et Marie Curie, designed an apparatus to snatch up the worms at the foot of a black smoker and maintain them under extreme pressure all the way to the surface, where they are transferred into a specially designed aquarium. 

Once in the lab, the specimens were subjected to three thermal regimes. One group was maintained at a balmy 20oC. A second had their environment  gradually increased to 42oC for two hours.  For the final group, the temperature was raised to 55oC for two hours, upon which point the worms would have been allowed to recover at 20oC if they hadn’t already been dead.

There was no discernible damage to the worms who were subjected to 42oC water. Not so with the unfortunate creatures who spent time at 55oC. Interestingly, the group that stayed at 20oC the entire time had a lower survival rate than the 42oC group.

While the Pompeii worm can withstand high temperatures, the reports of its heat tolerance are clearly exaggerated. Good to know.

Ravaux, J., Hamel, G., Zbinden, M., Tasiemski, A., Boutet, I., LĂ©ger, N., Tanguy, A., Jollivet, D., & Shillito, B. (2013). Thermal Limit for Metazoan Life in Question: In Vivo Heat Tolerance of the Pompeii Worm PLoS ONE, 8 (5) DOI: 10.1371/journal.pone.0064074.

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