Back From Pompeii
Over 20 years after marine biologists first discovered hydrothermal vents, another discovery was made. Close to the Galápagos Islands at the east Pacific rise, an organism was found. Withstanding higher temperatures than any other known species could endure. It is now known as the Pompeii worm. The Polychaete, Alivinella pompejana is a polyextremeophile. An organism able to survive in two or more extreme environment conditions. Pompeii was made famous when Mount Vesuvius erupted in 79AD, the Pompeii worm is only found deep underwater at hydrothermal vents where water temperatures can reach 400°C. How is this worm able to survive?
Before understanding the physiological and biochemical functions of the Pompeii worm we should look at what makes their habitat so extreme. Found 2600m deep, hydrothermal vents would be one of the least expected places to harbour life. Since the habitat is out of reach of the sun and under huge amounts of pressure from the overlaying seawater, the biological stress will be unlike any surface organism has experienced. It doesn’t stop there. These Pompeii worms get their name by living on the black smoker of a hydrothermal vent. This is where the hydrothermal fluids mix with cooler sea water, just like the tip of a volcano. The temperature of these fluilds are so high during the time surrounded by rocks they extract materials like sulphur, creating an extreme chemical gradient along with the temperature gradient. Thus creating a hot toxic environment, an environment the Pompeii worms chooses to live in.
Some hydrothermal vents are so abundant of the Pompeii worm that the tubes act as chimneys over the smokers. These multi layer tubes, formed by the worm itself with the aid of some symbiotic bacteria are comprised of inorganic and organic material. Consisting mainly of sulphur and proteins. It is thought that the ionic bonds between inorganic components act to stabilise the worm in these conditions, especially against the low pH levels that can be experienced around the smoker.
Since there is no sunlight 2600m deep at the east Pacific rise, another biological mechanism other than photosynthesis is required to produce energy. This is where chemosynthesis comes in, in the form of sulphur oxidation. The tubes of the worms are strategically placed over the black smokers to ensure a constant supply of reduced inorganic sulphur compounds. These compounds are then oxidised into sulphur to produce ATP, but this reaction is not carried out by the Pompeii worm. Instead symbiotic Prokaryotes which live in abundant quantitates within the tubes carry out the sulphur oxidation, this creates a chemosynthetic relationship. But it is unclear how the bacteria thrive apart from using the tube as refuge from heat and other harmful conditions.
More Aid From Bacteria
Various species of bacteria have been found within dwelling tubes of the Pompeii worm. One, known as Nautilla profundicola, an epibiotic bacteria with filamentous projections which can been seen to look like hair on the image of the Alvinella pompejana. This layer is able to act as insulation form the worm, just like hair insulates a polar bear. The layer is formed on the end and back of the worm due to these areas being located closest to the smoker where temperature will be highest. Since this layer is fairly thick compared to the size of the worm, it can also act as a shield as well as insulation. If a sudden change in temperature is experienced the bacterial could take the fall, in turn protecting the worm. This relationship is symbiotic, the worm repays the bacteria for protection by secreating a mucus. The bacteria thrives on this mucus.
Don’t Forget The Pressure
The Pompeii worm has been withstanding this heat in the deep sea, meaning it also faces extreme pressure. it’s ability to survive at either let alone both is incredible and might make the worm the hardest extremophile known.