Carl Woese

The man responsible for one of the biggest surprises in microbiology wasn’t even interested in biology when he was young. As an undergraduate, Carl Woese (1928- ) was excited by math and physics. He could hardly have cared less about microbes or how they were classified. But in graduate school at Yale, Woese found himself growing fascinated by evolution. In 1953, he received his PhD in biophysics and eventually decided that he would try to figure out the origin of the genetic code. The key, he thought, was in the ribosomes and associated molecules. So he decided to compare ribosomes from different species of bacteria. Before he could start, Woese needed to know how his bacteria were related – but he soon came up against a frustrating barrier.

For centuries, microbiologists had tried to classify bacteria and determine their evolutionary relationships. But by the 1970s, they had pretty much given up hope. As Woese puts it "…microbiologists couldn’t tell in general whether two bacterial strains were as closely related as rats and mice or as distantly related as birds and elephants." Instead of the familiar classification scheme using families and phyla, microbiologists had invented Bergey’s manual. In Bergey’s classification, bacteria are simply lumped into groups that have a similar appearance, enzymes and physiology. This scheme let Woese identify whether he had Escherichia coli or Pseudomonas aeruginosa in the test tube, but otherwise it was no help at all.

So Woese set out to find his own answers. He compared the ribosomal RNA (rRNA) of different bacteria to determine their evolutionary relationships. The more closely related two bacteria are, the more alike their rRNA should be. At first the work was very tedious; Woese’s laboratory could sequence the rRNA of only one or two organisms each year. But gradually the technology accelerated until they could compare a hundred organisms in a day.

As the information accumulated, Woese discovered that the bacterial world looked very little like Bergey’s manual. Bacteria in distant groups turned out to be close relatives - and sometimes bacteria in a single group turned out to be very distant indeed. But the biggest surprise was that one group of ancient organisms were not bacteria at all. These organisms, which often lived under extreme conditions such as high heat, looked just like bacteria. But their rRNA said otherwise. In the 1980s, Woese and his colleagues appalled many microbiologists by suggesting that instead of two basic divisions of life, bacteria and eukaryotes, there were three: bacteria, eukaryotes and these extreme organisms which they called the archaea. Even worse, the archaea seemed to be more closely related to eukaryotes than to true bacteria. At first, Woese met with skepticism – but, as the evidence has accumulated, things have changed. Although classification schemes are still being debated, there seems to be little doubt now that Woese was right. The University of Illinois scholar, who still carries out active research on both ribosomes and bacterial evolution, has become one of the most famous figures in microbiology.

  Sources

Harcourt College Publishers. 1999. Microbial evolution and diversity. A conversation with Carl Woese. Available at: http://www.harcourtcollege.com/lifesci/bioweb/depts/interviews/woese.html Accessed September 22, 2000.

Woese Carl R. Discovering the real microbial world. In: Atlas R.M. Principles of Microbiology. Dubuque, IA: Wm C. Brown; 1997:1092-1097.

[The source of the Woese quote]

University of Illinois Faculty Research in Microbiology: Carl R. Woese. Available at: http://www.life.uiuc.edu/Micro/woese.html Accessed September 22, 2000.