Decoding of Microbe’s Genes Sheds Light on Odd Form of Life

Scientists have decoded the genes of a microbe that lives on the ocean floor, can survive only in near-boiling water and thrives on carbon dioxide, offering new insights into a third major branch of life on Earth, experts say.

A team of researchers from three institutions announced that they decoded the 1,700 genes of a microbe called Methanococcus jannaschii and found that it is a member of an unusual branch of life discovered in 1977 called archaea.

“Two-thirds of the genes in this organism are new to science and biology,” said J. Craig Venter of the Institute for Genomic Research, the senior author of a study to be published Friday in the journal Science.

This study, he said, proves that the microbe is a member of a class different from the two other basic and most common branches of life--bacteria and eukaryotes, which include plants, animals and humans.

The existence of archaea as a third branch of life was first proposed by Carl Woese and Ralph S. Wolfe of the University of Illinois, Urbana almost 20 years ago.

Cellular structure is the main difference between these forms of life. The cells of eukaryotes have nuclear structures. Bacteria do not. Archaea have some characteristics of the other life forms, but are fundamentally different in the way they function and live, said Venter.

About 500 species of archaea are now identified and Venter said there may be a million others. The life form is thought to produce about 30% of the biomass on Earth, much of it in the Antarctic Ocean.

Archaea include microbes that live at the extremes of the planet--the very, very cold, hot or high pressure places that no other form of life could endure.

Some scientists have suggested that archaea may represent the earliest form of life and that they may be the most likely form of life existing on other planets. Their precise position on the tree of evolution is still uncertain, Venter said.