Swedish researchers have discovered a new source of silver. It isn’t a silver mine ? it’s Pseudomonas stutzeri, a kind of bacteria that lives in silver mines and produces minute crystals of silver. The discovery is especially surprising because silver is highly toxic to most microbes. But P. stutzeri get around this problem by gathering up the silver and storing it at the edges of their cells (see photo).

The researchers, from the Department of Materials Science at Uppsala University, cultured the bacteria and examined the silver crystals that were synthesized. Most were pure silver, but one group produced silver sulfide and another produced an unknown compound that may have contained hydrogen, carbon, nitrogen, and oxygen. The crystals had well-defined shapes, including triangles and hexagons (see photo below). [1]

It would take a lot of bacteria to produce enough silver to make just one small earring: the largest crystals measure a mere 200 nanometers. A nanometer is one billionth of a meter, or about 1/10,000 the thickness of a human hair. But while P. stutzeri may not generate much excitement among jewelers, they could be a breakthrough for materials scientists who work with substances called nanophase materials.

All crystalline materials consist of individual crystals, or grains, whose atoms are arranged in an orderly pattern. The atomic arrangement determines a substance’s color, strength, conductivity, and other properties. The crystals that make up nanophase materials are at least a thousand times smaller than “normal” crystals. [2] Although nanophase materials have the same chemical composition as their regular counterparts, the precise arrangement of their atoms makes them behave in very different ways.

For instance, nano-crystalline copper is up to five times harder than conventional copper. Titania, a common ceramic, is normally very brittle, yet its nano version is soft and squishy. [3] Such materials have seemingly unlimited potential for use in technology. In the case of silver, the Swedish researchers envision using the nano-scale crystals in metal films and coatings. For instance, they are developing a thin film that absorbs solar energy at a particular wavelength and could be used for energy-efficient heating.

So far, the biggest obstacle has been the time and cost involved in producing nanophase materials. Letting fast-reproducing bacteria do the work could speed up the process considerably. Moreover, researchers hope they’ll be able to customize the bacteria to grow particles of just the right size and shape needed for a particular use. First they’ll have to study the bacteria more closely to determine exactly how they manufacture the silver crystals. But in time, the lowly microbe may join the high-tech world of nanotechnology.

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