Symposium marks 30th anniversary of discovery of third domain of life

October 16, 2007

Thirty years ago this month, researchers at the University of Illinois published a discovery that challenged basic assumptions about the broadest classifications of life. Their discovery - which was based on an analysis of ribosomal RNA, an ancient molecule essential to the replication of all cells - opened up a new field of study, and established a first draft of the evolutionary "tree of life."

To mark the anniversary of this discovery, the university is holding a symposium Nov. 3-4 (Saturday-Sunday), with a public lecture at the Spurlock Museum on the evening of Nov. 2. "Hidden Before Our Eyes: 30 Years of Molecular Phylogeny, Archaea and Evolution" will detail the exacting work that led to the discovery of a "third domain" of life, the microbes now known as the archaea. The event will revisit the program of research that led to the discovery, explore its impact on the study of evolution, and describe the way in which genetic analysis continues to revolutionize biology, in particular microbial ecology.

In 1977, microbiology professor Carl Woese led the team that identified the archaea as a unique domain of life, distinct from bacteria and other organisms. Prior to this finding, generations of evolutionary biologists and microbiologists believed that the microbes now called archaea were simply another taxon among bacteria. They had divided all living organisms into two broad superkingdoms, or domains: the "prokaryotes," which included both the true bacteria and archaea; and "eukaryotes," including all animals, plants, fungi and protists (a diverse group that includes protozoans, algae, slime molds and other organisms). Some prominent biologists still hold to this classification scheme.

Woese had set out to map the evolutionary history of life by comparing RNA sequences of a molecular sequence common to all living cells: the ribosome, which manufactures a cell's proteins.

Each group of organisms contains sets of genetic sequences in their ribosomal RNA that are distinctive. These genetic "signatures" differentiate the groups. Woese's analysis of a variety of organisms' genetic signatures told a story that was different from the conventional wisdom, however.

This surprising discovery came when the researchers looked at the ribosomal RNA (rRNA) of a group of methane-generating microbes that had been classified as bacteria. Illinois microbiology professor Ralph Wolfe, an expert on these "methanogens," was a member of Woese's team, along with postdoctoral researcher George Fox, graduate student William Balch and lab technician Linda Magrum.

"Of all the numerous suggestions we had gotten for organisms to study, the one I solicited from my colleague, Ralph Wolfe, turned out to be the most important," Woese wrote in an account of the discovery. "Ralph was in the process of working out the biochemistry of methanogenesis, which made it natural for him to suggest we characterize the methanogens."

Wolfe was one of only a handful of researchers studying methanogens in the mid-1970s. These organisms were notoriously difficult to grow in culture because they could survive only in an oxygen-free atmosphere that was rich in hydrogen and carbon dioxide. Balch, a graduate student in Wolfe's lab, had found a way to create a sealed and pressurized atmosphere inside a test tube that would support these organisms, however. Using this technique, a methanogen now called M. bryantii, was grown in sufficient quantities for study.

Woese had already found a collection of rRNA sequences that were specific to bacteria, and another set of sequences unique to plants, animals and other eukarya. When he sequenced the ribosomal RNA of Wolfe's methanogen, however, he found that it was strikingly different from that of eukarya and bacteria. Although it shared some universal sequences with the other organisms, it also carried its own unique set of sequences that did not fit with either group. It was "neither fish nor fowl," Woese said.

The scientists were astonished, and quickly turned their attention to other methanogens. The genetic pattern held: The rRNA signatures of the methanogens were distinct from those of eukaryotes and bacteria. Woese concluded that the methanogens were not bacteria.

Wolfe recalled, "When Carl said they weren't bacteria, I said: 'Of course they are bacteria! They look like bacteria! They have this prokaryotic morphology and cell structure.' "

But when Wolfe saw how the sequence data fell into discrete groups, with all the methanogens in a category of their own, "I became a believer," he said.

Their findings were published in the Proceedings of the National Academy of Sciences in October 1977. The paper's three-sentence abstract stated simply that "the methanogens constitute a distinct phylogenetic group... only distantly related to bacteria."

A second PNAS paper, published the following month by Woese and Fox, outlined the evidence that there were three - rather than two - superkingdoms, or domains, of life.

"There was general amazement and feeling that something great had been discovered among the physical scientists," Woese said.

Many microbiologists and other life scientists were unwilling to accept the new classification scheme, however. They continued to see the archaea as a highly differentiated offshoot of the bacterial line.

In 2003, Woese won the $500,000 Crafoord Prize in Biosciences for his discovery of this "third domain of life." The prize, given by the Royal Swedish Academy of Sciences, marks accomplishments in scientific fields not covered by the Nobel Prizes in sciences, which the academy also selects.

Controversy over the work continued, however. Some scientists described the 1977 announcement of a third domain as an achievement comparable to that of the discovery of a new continent. Others discounted the idea as a "fantastic" hypothesis based on a limited and unreliable pool of data. To this day, many textbooks, dictionaries and other science reference materials include the "classical" and the Woese classification schemes.

Now 79, Woese continues his work as a member of the "Biocomplexity" theme at the Institute for Genomic Biology. He works with collaborators in physics, chemistry, geology and microbiology in a continuing exploration of the genomic complexity of biological systems. He worries about what he sees as a general lack of interest in evolution among microbiologists and other life scientists. And he hopes that a new generation of scientists will make full use of the genomic tools that he believes could revolutionize the study of the origins and evolution of life.
-end-
Wolfe, 86, an emeritus professor of microbiology, continues his interest in the physiology and biochemistry of the methanoarchaea.

More information about "Hidden Before Our Eyes," is available at the symposium Web site: http://archaea.igb.uiuc.edu.

To view or subscribe to the RSS feed for Science News at Illinois, please go to: http://webtools.uiuc.edu/rssManager/608/rss.xml.

University of Illinois at Urbana-Champaign

Related Bacteria Articles from Brightsurf:

Siblings can also differ from one another in bacteria
A research team from the University of Tübingen and the German Center for Infection Research (DZIF) is investigating how pathogens influence the immune response of their host with genetic variation.

How bacteria fertilize soya
Soya and clover have their very own fertiliser factories in their roots, where bacteria manufacture ammonium, which is crucial for plant growth.

Bacteria might help other bacteria to tolerate antibiotics better
A new paper by the Dynamical Systems Biology lab at UPF shows that the response by bacteria to antibiotics may depend on other species of bacteria they live with, in such a way that some bacteria may make others more tolerant to antibiotics.

Two-faced bacteria
The gut microbiome, which is a collection of numerous beneficial bacteria species, is key to our overall well-being and good health.

Microcensus in bacteria
Bacillus subtilis can determine proportions of different groups within a mixed population.

Right beneath the skin we all have the same bacteria
In the dermis skin layer, the same bacteria are found across age and gender.

Bacteria must be 'stressed out' to divide
Bacterial cell division is controlled by both enzymatic activity and mechanical forces, which work together to control its timing and location, a new study from EPFL finds.

How bees live with bacteria
More than 90 percent of all bee species are not organized in colonies, but fight their way through life alone.

The bacteria building your baby
Australian researchers have laid to rest a longstanding controversy: is the womb sterile?

Hopping bacteria
Scientists have long known that key models of bacterial movement in real-world conditions are flawed.

Read More: Bacteria News and Bacteria Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.