Extremophile

I

Introduction

Extremophile, organism that lives in extreme environments where other life forms cannot survive. The term extremophile means “extreme-loving” and such organisms need extreme conditions to thrive. The great majority of extremophiles are single-celled microorganisms that are species of archaea, bacteria, or algae. Some types of multi-celled algae, as well as fungi, lichens, protozoans, and invertebrates, are also considered extremophiles.

The habitats where extremophiles are found may have extreme temperatures (hot or cold), extreme chemical conditions (acidic, alkaline, salty, or toxic), extreme pressures, or extreme dryness; or they may lack oxygen or sunlight, or have high levels of radioactivity. Continuing discoveries of extremophile organisms have expanded the known size and diversity of the biosphere (life zone) on Earth.

II

Biology of Extremophiles

Many extremophile microbes are autotrophs that synthesize organic (carbon-containing) compounds to make their own food. Organisms that use chemicals such as hydrogen sulfide (H₂S) as an energy source (chemosynthesis) are called chemoautotrophs; organisms that use light (photosynthesis) as an energy source are called photoautotrophs. A few extremophiles are known to get energy from radioactivity.

Other organisms in turn may eat the self-sufficient extremophiles or feed off their waste or other byproducts. Extremophile microbes can become the basis of a food chain, a biological community, or an entire ecosystem, such as marine life around deep-sea hydrothermal vents on the ocean floor. The animals that live in the same environment as the microbes are sometimes called extremophiles, as well. Certain types of deep-sea tube worms and clams have a symbiotic relationship with extremophile microbes and obtain their food from chemoautotrophic extremophiles attached to their body tissues.

---

---

III

Study of Extremophiles

The identification and study of extremophiles are important areas of research in biology, microbiology, and biochemistry. Extremophiles can also provide clues to astrobiologists and other scientists about how life began on Earth or how life might exist on other planets or bodies in space. The unusual physical and chemical characteristics of extremophiles make such organisms potentially useful in industry, technology, and medicine.

Researchers are particularly interested in the special enzymes produced by extremophiles, sometimes called “extremozymes.” Enzymes are biological proteins that speed up chemical reactions. Once their chemistry and structure are understood, such extreme enzymes can often be made synthetically or can be further modified for use in manufacturing and other fields. Also of major interest is the ability of some extremophiles to repair or to resist damage from heat extremes or from radiation, or to expel, break down, or convert toxic substances. Deciphering the genomes of extremophiles may reveal special genes that such organisms have evolved.

IV

Extreme Environments for Life

Scientists continue to discover new environments in which extremophile life forms occur. Life may be possible in nearly any habitat on Earth in which liquid water exists and some form of energy is available. Extremophiles are often classified into different categories based on what kind of environment they live in. However, some types of extremophiles fit into more than one category and may be adapted to combinations such as high temperatures and chemical extremes.

	More from Encarta
	•  Presidential Myths Quiz •  Coffee break: Recharge your brain