Enzymes at the Extreme
Andrews, Ryan, The World and I
Derived from microbes that thrive in surprisingly hostile environments, newly discovered biological catalysts promise to revolutionize industrial processes.
For centuries, people have enlisted the aid of microbial entities to cater to their needs and comforts. Yeasts have been used for the preparation of bread and alcohol, and without certain bacteria there would be no cheese or yogurt. Natural substances derived from microorganisms have given us new and improved drugs to fight specific diseases, and enzymes isolated from a wide variety of microbes have proved useful in applications ranging from food processing to the catalysis of reactions in research laboratories.
But in the world of chemical and industrial processing, things can really heat up. Many procedures vital to industry are performed at high temperatures and pressures and involve chemical catalysts and solvents that are harmful to the environment. Although biological substances are environmentally "friendly," in the sense that they are biodegradable, their use in industrial processes has been limited by their inability to withstand harsh conditions. For instance, the extraction of petroleum and natural gas from wells through the process called hydraulic fracturing requires reactions at temperatures exceeding 100 [degrees] C (212 [degrees] F), while most conventional enzymes function well only up to about 50 [degrees] C (122 [degrees] F). In addition, most enzymes are sensitive to the high pressures and nonaqueous solvents employed in many commercial processes.
In the search for biological catalysts able to withstand such severe conditions, researchers and biotech companies are turning to a recently discovered dimension of the microbial world: microorganisms that thrive in surprisingly hostile environments, such as hot springs, freezing arctic waters, and deep-sea geothermal vents. These microbes have been dubbed extremophiles, and their associated enzymes are referred to as extremozymes. As more is being learned about the molecular biology of these unusual microbes and their enzymes, it is becoming increasingly clear that extremozymes' unique properties make them attractive candidates as catalysts in tough industrial environments--something unheard-of before.
Meet the extremophiles
The surprising discovery that certain microorganisms thrive in high-temperature environments dates back to 1982. In that year, Karl Stetter of the University of Regensburg, Germany, reported the isolation of microbes from marine volcanic vents near the coast of Italy [see "The Hottest Life on Earth," THE WORLD & I, February 1992, p. 270]. The vents are located on the ocean floor, where the water penetrates deep into the earth's crust, becomes geothermally superheated, and returns to the surface, bringing with it certain gases and minerals. The microbes that Stetter discovered, subsequently termed hyperthermophiles (or just thermophiles), were found in areas where mixing of the superheated water with the surrounding seawater produced temperatures close to 100 [degrees] C. Since then, many other hyperthermophiles have been isolated from aquatic geothermal vents and from terrestrial hot springs.
These intriguing discoveries flew in the face of much that microbiologists had previously learned about microbial growth conditions. Boiling and steam sterilization were standard measures to eliminate microbial contamination, yet here were microorganisms that not only survived such temperatures but actually seemed to require them for optimal growth. Indeed, these microbes failed to grow at the lower temperatures required by most known organisms.
What, then, are these extremophiles, and what distinguishes them from microbes that exist in more temperate environments? To answer this question, we must turn for a moment to the science of taxonomy: the study of the classification of living things.
In the 1950s, biologists classified organisms into five kingdoms: Monera (bacteria), Protista (later, Protoctista, comprising algae, slime molds, protozoans), Fungi (molds, mushrooms, lichens), Plantae (flowering and cone-bearing plants, ferns, mosses), and Animalia (vertebrate and invertebrate animals). …