For years it was thought that life couldn’t exist below a certain depth or above a certain heat. Now those limits turn out not to be limits after all. Bryan Appleyard looks into extremophiles
From INTELLIGENT LIFE magazine, May/June 2012
Russian scientists have now poured 60 tonnes of freon and kerosene down the four-kilometre bore hole that plunges through the ice above Lake Vostok in Antarctica. This will stop the hole freezing up during the long Antarctic winter. When summer comes, the Russian team will return to drill the last 100 metres and expose the surface of a lake that has been buried beneath the ice for at least 15m years. Eventually they intend to explore this lost world, a place unseen by human eyes, with a robot submarine.
The temperature of the lake is about -3°C, but the water remains liquid because of the pressure exerted by the ice sheet. The pressure should also have kept the water super-saturated with oxygen and nitrogen. Once we would have assumed that this cold, lost lake would be no more than a geological curiosity, a dead relic of the time when Antarctica separated from Africa and drifted south. Now we can be almost certain that it is full of life. Most of these creatures will be tiny single-celled organisms, microbes, visible only under a microscope. But they will have novel genetic structures, they will use previously undiscovered enzymes and they will have evolved unique survival strategies. They will be a class of creature now known as extremophiles, lovers of extreme conditions.
This is a biological category that was only discovered 40 years ago. Now we know that the Earth is teeming with these hyper-resilient microbes, organisms that can survive levels of heat, cold, pressure, radiation and salt or acid concentrations that previously would have been thought fatal to all living things. The study of these creatures is still in its infancy, but they have already broadened our conception of life on Earth and raised hopes of detecting life in space. The surface of Jupiter’s moon Europa, for example, is an ocean of ice, beneath which there could be inhabited lakes like Vostok. Extremophiles also offer a cornucopia of new medical compounds, primarily antibiotics, as well as almost indestructible enzymes that could transform chemistry at both the domestic and industrial scales.
Almost daily now, new extremophile species are discovered. Also in Antarctica, outside the prefabricated hut erected by Robert Falcon Scott at the start of his doomed expedition in 1911, there are drums containing diesel oil. The site has been preserved as an historic monument so the drums remained intact until, in the last few years, they started leaking. Professor Michael Danson, director of the Centre for Extremophile Research at the University of Bath, seized the opportunity to dig into the soil beneath these leakages.“Behold! We isolated organisms that were living off the diesel oil.” Such organisms could be used to consume oil spills like BP’s disastrous gusher in the Gulf of Mexico in 2010.
In the 1980s, Karl Stetter couldn’t get funding from his university, Regensburg in Bavaria, to pursue his obsessive search for organisms that lived in temperatures higher than 60°C. The authorities just didn’t believe such creatures existed. So he took a holiday on the island of Vulcano off Sicily. First, he used his hotel shower to accustom his hands to very hot water. Then he dived off a rubber boat manned by his wife and daughter and took samples from the hot vents on the seabed. He took the samples back to his lab and discovered an organism that reproduced happily at 100°C. The world record for thermophiles—heat lovers—is now just above 120°C.
In the early 1990s, the prevailing microbiological wisdom said that the biosphere ended 7.5 metres beneath the seabed. Undeterred, John Parkes, now head of the School of Earth and Ocean Sciences at Cardiff, began to look for life in deep ocean cores, obtained by specialised drilling ships. Of the cores he acquired from around the world, two stood out. They were to make him one of the leading extremophile researchers in the world. The first came from just off the Peruvian coast, the other from near Newfoundland, the point where the continents first tore apart to form the Atlantic Ocean. Off Peru he immediately found life at 80 metres, overthrowing the orthodoxy. Later, off Newfoundland, he found life at 1.6km beneath the seabed. “That’s the record so far,” he says, “but we think we might be able to get down to 4km.”
Picture: The black smoker—the Saracen’s Head hydrothermal vent, 3,100 metres below sea level in mid-Atlantic. The picture was taken from Alvin the submersible (Science Photo Library)