Hydrothermal Vent Ecosystem
Geological Survey of India,
Marine Wing, Mangalore - 575 001
In 1977, the e citing discovery of hydrothermal vents was made by the scientists diving in Alvin to the Galapagos spreading center in the eastern Pacific off Equador, who were greeted at a depth of about 2.5 km by a spectacular sight of clouds of what looked like black smoke gushing out from tall chimneys on deep ocean floor (‘black smoker’). More exciting however, was the totally unexpected discovery of a lush community of exotic and unusual sea life – giant tube worms, huge clams, mussels etc thriving around the hot springs, which changed our understanding of planet Earth and life on it. The waters around the deep ocean hydrothermal vents as hot as 3800C are home to a unique ecosystem. The organisms that are common to vents include various forms of microbes – bacteria and archaea, and macrofauna – mussels, crabs, shrimps, worms, anemones, fish, octopus, snails, limpets and so on. H2S-oxidising bacteria, which live symbiotically with larger fauna, form the base of the ecosystem’s food chain. The energy source that sustains this deep ocean ecosystem is not sunlight, but energy from chemical reactions (chemosynthesis). Hydrothermal fluids coming out from vents contain H2S – an element lethal to most organisms. But vent microbes not only survive it, but depend on it for the survival of the entire ecosystem. The vent microbes get energy by breaking down H2S and they use this energy and oxygen to convert CO2 to sugars.
Vent fauna live at extreme conditions of no sunlight, tremendous pressure (300 atm), very high temperature (highest measured vent temperature is 4030C) and very acidic vent waters (pH as low as 2.8). Discovery of vent ecosystem altered our assumption that all ecosystems are dependent on sunlight and photosynthesis. The fact that life can exist without sunlight means possibility of finding life on other planets. Biomass as well as diversity of species in vent ecosystem is as high as that of a rain forest and life forms are both bizarre and ancient. Most vent fauna are new to science, and many of them are found nowhere else, and cannot exist outside vent conditions.
Giant tube worms are one of the most amazing animals that live in vent ecosystem. They grow up to 3 m long and 10 cm in diameter and more than 33 inches per year, making them the fastest growing marine invertebrate. They have a head, collar, trunk, and anchor, but no mouth, eyes or gut. Tubeworms contain a unique form of haemoglobin that transports both H2S (absorbed by the worm’s plumes from vent fluid) and O2 (absorbed from cold water) to endosymbiont bacteria. Billions of bacteria living inside the tubeworm produce sugars from CO2, H2S and O2.
Pompeii worm(Alvenella pompejana) – an organism that has only been found in hydrothermal vents, living close to the vent than any other species, ranks as the most heat-tolerant among higher order life forms. The worm resides in tubes. When in tube, the worm’s tail end basks in water as hot as 800C, while its head rests in water that is much cooler, about 200C. The grey fleece or ‘hairs’ on the worm’s back are actually bacteria, which act as protective thermal blanket for the worm and also detoxify the lethal toxic chemicals.
The first creatures to appear at a vent are bacteria that come up with the hydrothermal fluids, sometimes so densely that the vent looks like a ‘snow blower’. The 1991 discovery of snow blower vents blasting white bacterial matter into the ocean opened up another previously unimagined possibility – the existence of a sub-sea floor microbial biosphere, which may be as large as the biosphere on earth surface. By studying microbes in hydrothermal vents, scientists learn how life may develop and survive in extreme environments on earth and other planets. Many scientists believe that hydrothermal vents are the cradle, where life originated 3.5-3.8 Ma ago.
Vent organisms have wide industrial and medical applications. They may be useful to combat industrial pollution (H2S) and clean up sites contaminated with Cu, Cd, Hg etc. They may help in development and manufacture of new heat resistant industrial chemicals and new drugs to combat germs now resistant to now plant and soil based drugs. Methanogenic (methane- producing) archaea could provide a renewable source of natural gas. Giant tube worms may help us understand and combat deadly human iron deficiencies. Extremozymes – enzymes produced by heat loving extremophiles like vent microbes have great potential in biotechnology. Proteins and enzymes of ultrathermophilic archaea in hot vent waters have unusually high thermal stabilities and hence, such enzymes are expected to have longer shelf life, produce less waste, and have lower risk of contamination. They will also permit reactions to run hotter, faster and purer, and will be biodegradable. Extremozymes may thus help (i) make dry oil wells productive by thinning oil now too thick for extraction (ii) convert corn starch to sugar (iii) allow anaerobic bioremediation (iv) production of a biocomputer chip and (v) a host of other industrial processes by speeding up biological and chemical reactions.
Vent bacteria possess special proteins - eurythermal enzymes that function effectively in a wide range of temperatures. They find applications in pharmaceutical, textile, paper and detergent industries.They act as catalysts to break down fats, wood etc, as well as DNA and operate in organic solvents. The most commonly used DNA polymerase in PCR (Polymerase Chain Reaction – a technique used to amplify and clone DNA) is Taq DNA polymerase, isolated from Thermus aquatics, a bacteria from hot springs of Yellow Stone National Park. But, for a few PCR applications, the lack of proof reading by Taq DNA polymerase is a problem. DNA polymerase isolated from Thermococcus littoralis, a microbe from deep-sea hydrothermal vents have proof reading activity. This DNA polymerase, marketed as ‘Vent DNA polymerase’ has now 30% market share in DNA polymerase sales. The discovery of life in deep sea hydrothermal vents revolutionized ideas about where and how life could exist. But it also raised questions that never entered our minds before: How can so much life thrive at the sunless sea floor? What special features do the organisms have to live at deep sea vents? What else might be living at the sea floor or below it, or in environments in other planets that once we thought were too extreme to support life?