Forget ancient maps and metal detectors. Those seeking hidden gold might do well to add bacteria to their toolbox. The bacterium Delftia acidovorans secretes a molecule that binds to dissolved gold and turns it into shiny, solid gold, scientists have discovered. The bacterium — and perhaps others like it — might one day process gold at mining sites or create gold nanoparticles with desirable properties, says geomicrobiologist Frank Reith, a research fellow at the University of Adelaide in Australia. In 2006 Reith and his colleagues reported finding biofilms of bacteria growing on solid gold grains in soil. Some of these...