They can withstand a broad range of temperatures - some close to the boiling point, eat toxic chemicals for breakfast, bear the weight of the ocean on their shoulders, and never see the light of day. Such is the life of the organisms that inhabit deep-sea hydrothermal vent sites! These creatures, from microscopic bacteria to towering tubeworms, thrive under some of the most demanding conditions on the planet. And what further distinguishes them from other life on Earth is their energy source. They are the only complex ecosystem known to live on energy from chemicals rather than energy from the sun. On land, our food chain is based on photosynthesis, the process by which green plants use the energy from the sun to make food. However, in the deep sea, where the sun's rays never reach, organisms make food from chemicals - a process called chemosynthesis. Tiny Bacteria Play Mighty Role The hydrogen sulfide and other chemicals that rocket out of hydrothermal vents would be poisonous to most organisms. But tubeworms and other animals flourish here thanks to special adaptations and the relationship they have with the tiniest life at the vents: bacteria. Bacteria hold the key to life at the vents because these microscopic organisms can convert the toxic chemicals released by the vents into food and energy. So in order to survive, vent-dwelling animals, such as clams and tubeworms, must either consume bacteria or harbor bacteria in their bodies so that the microbes can make food for them. For example, tubeworms have no mouth, eyes, or stomach ("gut"). Their survival depends on a symbiotic relationship with the billions of bacteria that live inside of them. These bacteria convert the chemicals that shoot out of the hydrothermal vents into food for the worm. Since a tubeworm has no mouth, how do bacteria enter the worm? Scientists have found that, during its earliest stages, the tubeworm does have a mouth and gut for bacteria to enter. But as the worm grows, these features disappear! New Scientific Discoveries Scientists are particularly interested in bacteria from hydrothermal vents because these microscopic organisms possess enzymes that can withstand high temperature and pressure, giving them many valuable uses in industry. For example, some bacteria can convert harmful chemicals to safer forms, making them ideal for cleaning up oil spills and hazardous waste. Scientists are also curious about the deep sea's tiniest life because these organisms are among the oldest on Earth. In fact, Archaea (pronounced "ark-ee-uh"), an ancient life form, recently was found at vent sites. Previously, these microscopic organisms had been discovered in another "extreme environment" - hot springs in Yellowstone Park. Like bacteria, Archaea consist of cells without a nucleus, yet more than half of their genes are unlike anything else on the planet!     "Fingerprinting" Microbes During a research cruise, scientists grow microbes taken from the deep sea in artificial media supplemented with various chemicals. The microbes are then incubated at temperatures up to 100°C (212°F) and examined for growth. One of the ways that scientists try and understand how extreme environments support life is by investigating the smallest known organisms that inhabit them - microbes. Microbes are microscopic, single-celled organisms without a nucleus. These organisms, which include bacteria and viruses, form the base of the food chain. They can exist under conditions that would be lethal to most organisms. For instance, there are bacteria that can grow at 113°C (235°F) and pressure as high as 250 atmospheres. They also can flourish under extremes of pH, toxic metal concentrations, and even radioactive chemicals. At the University of Delaware, scientists are studying the microbes that exist in association with hydro-thermal vent chimneys. Using the deep-sea sub Alvin's manipulator arms, the scientists collect samples and bring them to the surface. The microorganisms are then studied n more detail by growing them and analyzing their DNA. After extracting DNA from the cells, we compare the unique sections of their nucleotides (compounds that make up DNA) to classify the microbes. This technique, sometimes known as genetic fingerprinting, is a useful tool for learning how the microbes are related to one another as well as for identifying their distinctive properties. Why do we culture microbes? Biotechnology - Microbes from extreme environments have enzymes that can withstand high temperature and pressure, giving them many biotechnological and industrial uses. Some microbes can convert harmful chemicals to safer forms, making them ideal for use in bioremediation. Origin of Life - Microbes can give us clues to when and where life was formed on Earth. The most primitive microbes live in high-temperature environments such as hydrothermal vents. By finding the oldest microbes of all, we hope to visualize the type of environment that existed when life was formed on Earth. See translation to Haitian Creole courtesy of Susan Basen.