Swedish scientists have reported the synthesis of silver crystals by a bacterial strain, Pseudomonas stutzeri, originally isolated from a silver mine (Proc. Natl. Acad. Sci. 96, 13611–13614, 1999). Silver is usually very toxic to microbes and has even been used as an antimicrobial agent. Although metal-resistant microbes have been found before, the mechanism of resistance more commonly involves actively pumping the toxic ions out of the cell. These workers, led by Tanya Klaus, found that by culturing the bacteria in the presence of high concentrations of silver salts, they could create crystals of well-defined compositions and shapes in the region surrounding the plasma membrane. The size of the crystals identified by these workers (up to 200 nm) suggests that they might eventually be used for the formation of thin metal films to absorb solar energy or to construct nanometer scale materials with unique optical and electrical properties useful in microelectronic applications. More traditional approaches to nanoscale synthesis tend to be inefficient and produce toxic by-products and the Pseudomonas system could represent a useful alternative. Klaus cautions, however, that the mechanism of the crystal formation needs to be better understood, before any practical application of the bacteria could be envisaged.