SCIENCE / MEDICINE : Bacteria Produce an Unusual Magnet for Navigational Use : Origin of life: The discovery should shed new light on how animals came to produce shells, teeth and bones. And the process may be much older than previously thought.

Bacteria that orient themselves in the Earth’s magnetic field by using tiny iron sulfide magnets have been discovered in Morro Bay by researchers at Cal Poly San Luis Obispo.

Many species of bacteria and animals--and perhaps even humans--are known to use embedded particles of magnetite, a form of iron oxide, for navigation. But the new bacteria, whose discovery is reported today in the British journal Nature, are the first using sulfur-based magnets.

Understanding how the newly identified bacteria produce the unusual magnets should shed new light on the mechanism of biomineralization, by which animals produce shells, teeth and bones.

Furthermore, the presence of iron sulfide magnets suggests that the process of biomineralization began much earlier in the Earth’s history than had previously been believed, when hydrogen sulfide rather than oxygen was the most important component of the atmosphere.

The discovery “gives us a new line to follow back to the origin of life,” said chemist R. J. P. Williams of the University of Oxford in Britain.

It also “means that biomineralization is a much more sophisticated process than we had previously thought, and possibly much older as well,” said physicist Richard B. Frankel of Cal Poly, one of the report’s authors.

In a separate paper, researchers from the Brazilian Center for Physics Research in Rio de Janeiro report that they have found other bacteria containing different magnetic iron sulfides.

Until recently, biologists believed that biomineralization began about 600 million years ago, when the first shells appeared in fossils. Magnetite-containing bacteria have subsequently been dated back 2 billion years. The new discovery could extend the origin of biomineralization even further back into the Earth’s 4.5-billion-year history.

“It’s a very exciting discovery,” added geobiologist Joseph Kirschvink of Caltech.

The first magnet-containing or magnetotactic bacteria were discovered in a brackish Massachusetts marsh in 1975 by Richard P. Blakemore, now at the University of New Hampshire. Placed in a magnetic field, the bacteria swam toward the north.

The bacteria live primarily in sediments on the bottom of marshes, where they feed on the rich detritus of other organisms. At the latitudes where the bacteria were discovered, the Earth’s magnetic lines of force running northward dip into the Earth at a shallow angle, leading the bacteria downward toward the rich food sources on the bottom. Magnetotactic bacteria in the Southern Hemisphere swim toward the south, which again points them toward the bottom.

Researchers have subsequently discovered magnetotactic organs in the bellies of honeybees and in the brains of birds, tuna, whales and dolphins. Some evidence suggests that similar organs might even be present in humans. The magnetotactic organs, in combination with visual cues from the sun, help the animals navigate during migration.

In all previous cases, however, the magnetic organs have been based on magnetite. The new discoveries represent the first time sulfur-containing magnets have been observed. Frankel and his colleagues isolated the bacteria from environments that have high sulfide concentrations, such as the ponds, lagoons and marshes that line the Central Coast of California.

Geophysicist Darci Motta S. Esquivel and his colleagues in Brazil isolated their bacteria from similar locations in South America.

Kirschvink speculates that the iron sulfide deposits originally arose in bacteria as a method for storing iron, “which is crucial for any living organism’s metabolism.” Over time, the bacteria could then have evolved ways to use the material’s magnetic properties as well. Eventually, the same biochemical mechanisms evolved to produce shells and, later, teeth and bones.

The sulfide materials have not yet been found in fossils, he added, because they are “notoriously unstable chemically,” breaking down into simpler compounds such as iron pyrite, or fool’s gold. Interestingly, both Frankel’s group and the Brazilians found iron pyrite particles in the new bacteria. Their function is not yet known.

Oxford’s Williams believes that the iron sulfide compounds may also have played a role in the bacteria’s capture of life-giving energy from the environment, and he speculates that similar organisms may exist in the hydrogen sulfide-rich thermal vents that have been discovered on the oceans’ bottoms.

Concludes Williams: “There could well be a huge variety of life in the sulfide-rich zones on Earth, perhaps holding fresh clues to help answer the question of how life began.”