Microbes craft unusual crystals

In the flooded tunnels of an abandoned iron mine below the town of Tennyson, Wis., scuba divers recently retrieved a curious community of bacteria that grow bizarre, hairlike crystals. “The crystals look like tangled spaghetti,” says earth scientist Jill Banfield of the University of California, Berkeley. Now, Banfield and her colleagues have figured out how the bacteria produce these structures, a discovery that could help scientists design new materials and provide clues to possible life on other planets.

MICROBIAL SPAGHETTI. Bizarre crystals secreted by mine-dwelling bacteria. G. De Stasio/UW–Madison

Working with scientists at the University of Wisconsin–Madison, Banfield and her colleagues used X rays and electron microscopy to study the microbes’ chemical processes. The images revealed that the bacteria secrete polymer filaments from their cell walls. Iron oxide dissolved in the mine’s water then precipitates on the filaments to form a type of crystal called akaganeite. Described in the March 12 Science, each crystal measures only a couple of nanometers wide and up to 10 micrometers long.

The researchers hypothesize that the bacteria use the crystals to generate energy for the cell. The chemical reactions by which the crystals form produce an excess of protons on the surface of each bacterium. These protons then feed the cell’s energy-generating molecular machinery.

The new work could help scientists identify forms of life that might once have thrived on the iron-rich planet of Mars, says Banfield.

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