Bacteria strike gold

More than a decade ago, geochemists studying how gold grains form encountered a mystery. On the surfaces of gold grains and nuggets collected at several sites in Australia and the Americas, they detected microscopic, gold-encrusted structures shaped suspiciously like mounds of bacteria. But were they really bacterial remnants? And if so, were bacteria somehow playing a role in the formation of gold?

To unravel the mystery, Frank Reith, a geomicrobiologist at the Cooperative Research Centre for Landscape Environments and Mineral Exploration in Kensington, Australia, and three colleagues collected gold grains from two Australian mines. Most of the grains bore the distinctive mounds, they discovered, and the mounds were covered with a thin layer of slime rich in bacteria. DNA analysis showed that each grain harbored as many as thirty species of bacteria that were distinct from the species in the surrounding soils. One species, almost certainly Ralstonia metallidurans, was present on all the grains.

Subsequent experiments showed that the ubiquitous R. metallidurans can pull dissolved gold--which is highly toxic to most life forms--out of solution and precipitate it as harmless particles of solid gold. The details of the process remain to be understood, but in nature it enables the bacteria to live in toxic soils and to contribute to the creation of solid gold. (Science 313:233-6, 2006)

COPYRIGHT 2006 Natural History Magazine, Inc.
COPYRIGHT 2008 Gale, Cengage Learning