Gene tool may crack open microbial secrets.

In a world without microorganisms, dead trees would keep their carbon to themselves. Although the trees would still die, topple, break into small particles, and eventually be buried, they would not liberate this element, an essential building block of life. It takes methane-producing microbes like some archaea to turn carbon into methane gas, which they release into the atmosphere.

Scientists have now invented a genetic tool that may help them discover how archaea, a poorly understood form of life, accomplish this elemental task.

Last summer, researchers sequenced the entire genome of Methanococcus jannaschii, a methane-generating species of archaea living on the ocean floor (SN: 8/24/96, p. 116). That feat provided an inventory of the microbe's genetic instructions, but understanding of the inventory remains incomplete.

Of the reported 1,738 genes in M. jannaschii, only 44 percent resemble genes from known organisms other than archaea. The new tool, described in the March 18 Proceedings of the National Academy of Sciences, will enable scientists to discover the functions of the unidentified genes in M. jannaschii and in a broad collection of other methane-producing archaea.

"We haven't really been able to get at a lot of how these organisms live and grow," says William W. Metcalf, a microbiologist at the University of Illinois at Urbana-Champaign. "This is the first breakthrough that's going to help us do that."

Metcalf worked with colleagues at the University of Illinois and the University of Maryland at Baltimore to develop the new genetic tool, which he thinks will help researchers figure out how archaea convert carbon to methane.

Scientists' understanding of archaea lags far behind their knowledge of other microorganisms. Before 1977, biologists lumped archaea with bacteria. Then, Carl R. Woese of the University of Illinois argued successfully that archaea deserved their own branch on the tree of life.

The new tool consists of a small ring, or plasmid, of archaea DNA to which the researchers added a gene for resistance to antibiotics. The scientists can add to the plasmid whatever genes they need for their experiments and then insert the plasmid into an archaea. The plasmid can even carry genes from one species of methane-producing archaea to another.

William Whitman, a microbiologist at the University of Georgia in Athens, called the development "an extraordinary contribution." Scientists have had only two other genetic means of studying archaea, neither of which helped them examine the methane-producing group, he says.

"These guys are really highly specialized," he says of the methane producers.

Such archaea live in environments ranging from decaying teeth to the intestines of animals, acid baths, and boiling water thousands of feet beneath the sea. Scientists hope to learn how these different archaea perform their common function and how they survive extreme conditions, Whitman says.