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"Miracle" Microbes Thrive at Earth's Extremes

John Roach
for National Geographic News
September 17, 2004
 
For the past 30 years scientists have scoured the most inhospitable environments on Earth searching for life. Just about everywhere researchers look, they find it thriving in microscopic form.

These organisms, known as extremophiles, snuggle up to scalding hydrothermal vents in the Pacific Ocean. They cling to ice in Antarctica. They burrow in the high deserts of Chile and wallow in salty lake beds of East Africa.

Scientists continue to search for—and find—extremophiles everywhere from volcanic cauldrons in Russia to alkaline waters in China's Inner Mongolia. In the process, researchers are also beginning to tease out the organisms' secrets to life.



"We know that we are only scratching the surface of what is out there. At the same time, many people are trying to decipher how these organisms function," said Kenneth Stedman, a biologist with the Center for Life in Extreme Environments at Portland State University in Oregon.

Earth's most extreme environments are thought to resemble those on distant planets. Discovering organisms that thrive in such conditions broadens our understanding of the limits to life on Earth. Organisms also provide clues on where to search for extraterrestrial life.

Learning how extremophiles thrive has led to a variety of innovations. Scientists have developed novel compounds for the development of new drugs and enzymes that make better laundry detergents, cleaner paper production, and hydrogen for fuel cells.

"Experimentally, we are coming of age," said Frank Robb, a molecular biologist at the University of Maryland Biotechnology Institute in Baltimore.

Robb is the chair of Extremophiles 2004: Fifth International Conference on Extremophiles, a five-day gathering in Cambridge, Maryland, that begins Sunday. He expects about 320 scientists from around the world to attend the meeting to discuss the latest advances in the field.

Conference

So what constitutes an extremophile? Other than the fact that all extremophiles are microbial, there is no common bond that defines an extremophile, according to Stedman, the Portland State University biologist and a conference co-chair. Rather, the differences that distinguish extremophiles from the more mundane mesophiles (organisms that live in "normal" climates and environmental conditions) are subtle.

By deciphering the genomes of extremophiles, scientists are now making their greatest advances in this field. For example, researchers have identified the subtle differences that allow the cell walls of certain microbes to hold up at temperatures above 212 degrees Fahrenheit (100 degrees Celsius).

"Genomics has made a very significant contribution to the modus operandi of all extremophile fields," Robb said.

Genomics are the primary focus for the upcoming extremophile conference. Participants will also focus on a class of microbes known as the archaea, which literally means "ancient." Archaea differ enough genetically from bacteria to warrant their own branch on the evolutionary tree of life.

Many archaea are extremophiles. Scientists believe archaea resemble the earliest forms of life on Earth.

Archaea split off from bacteria some four billion years ago. Ancestors that split from archaea evolved into eukaryotes—life-forms, including humans, whose cells have nuclei.

Archaea are more similar to eukaryotes than bacteria, but much simpler and easier to analyze than eukaryotes. Their study, as a result, has made important contributions to understanding how eukaryote DNA is repaired and copied, Robb said.

Such insights may lead to better treatments for diseases like cancer, since progression of the disease relies on DNA replication and cell division on a continual basis.

Archaea are also providing scientists insight to the process of how proteins are built inside cells. "Some outstanding discoveries have been made," including pyrrolysine, the 22nd amino acid known to science, Robb said.

Amino acids are the key building blocks of proteins. Scientists once thought only 21 amino acids existed. But in 2002 a group of researchers discovered a new amino acid, pyrrolysine, while studying extremophiles that produce methane or natural gas as a by-product of energy generation. The find indicated that the genetic code is more flexible than originally thought.

Hyperthermophiles

One of the more eagerly anticipated talks at the upcoming conference will be given by Karl Stetter. A microbiologist at the University of Regensburg in Germany, Stetter is recognized as one of the world's greatest extremophile hunters.

"I will concentrate on hyperthermophiles, which are the most extreme of all extremophiles and which represent my field of interest for 25 years," he said.

According to Stetter, hyperthermophiles are unusually shaped archaea. Some look like snakes. Others resemble yeastlike spheres and cobwebs. All require extreme heat for their survival.

Stetter will also talk about nanoarchaea, which he describes as "a novel kingdom of dwarfy archaea," and the first genome sequenced from the group. "The Nanoarchaea appear to be very ancient symbionts," he said, referring to life forms that live symbiotically with others, "most likely existing since the earliest days of life."

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