Some Like it Hot!
(July 10th, 2013) How much heat can you bear? In the case of a Pompeii worm, it’s a lot - but not as much as previous studies have led us to believe. French researchers recently developed a new system to investigate the real thermal limit of the deep-sea annelid.
Alvinella pompejana, commonly called Pompeii worm after the Roman city Pompeii, due to its alleged high heat tolerance, are normally found attached to hydrothermal vent chimneys along the East Pacific Rise. There, they build papery tube colonies. Discovered only in the 1980s, the worms have already gathered quite some attention, as they are considered to be among the most heat-tolerant complex animals. Fascinatingly, they keep their tails inside their piping hot (up to 80°C) home tubes but their feathery heads hang out of the tubes into 22°C, almost chilly, waters.
The upper thermal limit of this worm has become a much discussed topic - reports suggest it can tolerate temperatures up to 80°C, which would make it the most thermo-tolerant marine metazoan. But testing how much heat it can really bear has been difficult, so far, as the worms hardly ever survived recovery from 2,500 meters depth due to “collection and depressurization trauma”. But a new “high-pressure aquarium” developed by Bruce Shillito and colleagues from the University Pierre and Marie Curie, France, will make more detailed in vivo studies on the Pompeii worm’s heat tolerance possible.
When asked about the chronology of events, Bruce enthusiastically shared the long story of this project. Their dream project was launched in 2006, when the team applied for funding for BALIST (Biology of ALvinella, Isobaric Sampling and Transfer). After three trials, they finally got it approved in 2008. For a layman or anyone apart from a marine biologist, BALIST is nothing but a high pressure or pressure-controlled aquarium, remarks Bruce, but, for the initiated, it’s a landmark modification, which provides tremendous aid in collection of live worms from the sea and their transfer to the lab.
In 2009, the team began designing the BALIST prototype; simultaneously they "fished" for heat shock proteins 70 (hsp 70) as they respond to environmental stresses like temperature. The maiden voyage took place in 2010, during which the prototype was put to the test. “Unfortunately,” says Bruce, “biological samples were then in too low numbers to obtain final results but we had enough to test our analytical methods for hsp fishing, while we gained some experience on optimal sampling in situ.” One of the reasons for their slim pickings was a natural spectacle. “We lost several days of work at sea because of the Eyjafjalljökull volcano eruption in May. We were all (ship and submersible turnover crew, and scientists) grounded in France for a whole week!" Thus, “the volcano protected Alvinella’s secrets”, jokes Bruce. Only the second cruise was successful and gave them enough results for the recent PLoS publication. The BALIST system allowed them to perform the long-awaited in vivo experiments to be carried out under controlled temperature at in situ pressure, which finally provided the first empirical demonstration of A. pompejana’s thermal limit: Exposure of two hours in 50-55°C hot water resulted in tissue damage and cell death – consequentially, the worms did not survive. This means that Alvinella’s upper thermal limit must be below 55°C. It's not as much as previously thought but nevertheless, the worms’ thermal optimum is above 42°C, which still places it among the most thermo-tolerant metazoans.
After publishing their results, the team has not sat back and relaxed but is all set for its next venture, in which they are planning to obtain wide-range transcription profiles of genes involved with heat tolerance. “Hopefully, this helps us understand the molecular response of animals facing heat,” says Bruce. The team is optimistic that their finding has a lot of value and they are proud of this new method of sample collection. “The isobaric collection (PERISCOP sampling cell) combined to isobaric transfer in a proper experimental ‘aquarium’ (BALIST) opens the way to study deep-sea fauna, including several fishes, which have never been sampled alive due to pressure differences,” says Bruce. But that pressure has now been taken off the scientists.
(1) Alvinella pompejana, National Science Foundation (University of Delaware College of Marine Studies)
(2) Bruce Shillito (left) and Gérard Hamel, both working on the Balist isobaric transfer system, during the Mescal 2 cruise. M. A. Cambon-Bonavita.