Even today, the legacy of the Cold War leaches into the waters of Colorado. Uranium, freed from the earth and destined for nuclear weapons, now contaminates the groundwater beneath several Colorado mines. But at some of these mines, a most unusual clean-up crew is at work. Lashing about with long electric cables connected to their own bodies, they remove dissolved uranium from the water. Each one of these janitors is just a thousandth of a millimetre across. They’re called Geobacter. They’re bacteria.

The handful of Geobacter species are recent discoveries. The first one, G.metallireducens, was discovered in the Potomac River in 1987. Another, G.sulfurreducens, was later found in oil-soaked Oklahoman soils. The group has the remarkable and useful ability