"We are dealing with microbes that probably oxidize ferrous iron and reduce oxygen," says Banfield. "The product, ferric iron, then precipitates. The precipitation occurs on microbial polymers attached to the cell."
The results, says De Stasio, are crystal structures of bizarre form: "The microbes produce a bunch of noodles, filaments on the cell surface, and at the core of the filament is a crystal. These polymer filaments extruded by the cells template the formation of these incredible crystals."
The new discoveries were made with the help of recreational scuba divers who routinely retrieve biofilms growing in the flooded tunnels of the Piquette Mine in Tennyson, Wis., for scientific analysis. These newfound crystal-making organisms occur in pumpkin-colored biomineral accumulations and in the water column of the flooded mine, according to Banfield.
She notes that microorganisms are known to make crystals for a variety of purposes. For example, some bacteria make magnetite to aid navigation, and others use their powers of biosynthesis to sequester toxic metals such as uranium.
But the structure of the crystals made by the microbes in the Piquette Mine was unexpected, "given the conditions under which they formed," Banfield says. "We attribute this to the effect of the polymer. They are different from virtually all other crystals in their aspect ratio."
Using a novel X-ray microscope to analyze samples retrieved from the mine, De Stasio and her group were able to observe the chemical interplay between the microbial polymer and the crystal.
Their detailed portrait of how the polymer strand is chemically bound to the crystal suggests that a templating process governs the synthesis of the slender crystals. The use of templates is widespread in nature. However, how animals and microo
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Contact: Gelsomina De Stasio
pupa@src.wisc.edu
608-877-2000
University of Wisconsin-Madison
11-Mar-2004