A bacterium's silver touch.

Silver is highly toxic to most microbes. Nonetheless, researchers have discovered several strains of bacteria that thrive in silver-laced ore deposits. Materials scientists now report that one of these metal-munching bacterial strains can synthesize silver-containing crystals with well-defined compositions and distinct shapes, including equilateral triangles and hexagons. Tanja Klans and her colleagues at Uppsala University in Sweden describe their findings in the Nov. 23 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES.

Up to 200 nanometers across, the crystals are embedded between a bacterium's plasma membrane and outer cell wall. One type of crystal is almost pure metallic silver, and another is largely silver sulfide. "The cells can accumulate silver in large quantities," the researchers say.

The results provide new insights into microbe-metal interactions. They also suggest direct biosynthesis as a potential route for producing silver-based, nanometer-scale particles for microelectronic devices and other applications. "The possibility of synthesizing metal particles directly in an organic matrix points toward new uses of metal-containing bacteria as precursors in thin films and surface-coating technology," the researchers note.