The Midas
bug (Ralstonia metallidurans) plays a significant role in the
formation of secondary
gold grains. Ralstonia
metallidurans could precipitate gold out of a solution, which may be
used as a means to bioprocess gold ores.
Dr. Frank Reith, a geomicrobiologist at the Cooperative Research Centre for Landscape Environments and Mineral Exploration (CRC LEME) in Australia, may have struck gold with his discovery – a bug that appears to play a significant role in the formation of secondary gold grains. Aptly named the Midas bug, the
bacteria were found on small
grains of gold in two mining sites more than 3,000 kilometers apart. Examined under a special laser-scanning microscope, the gold grains were found to be covered with biofilms, which actually consist of bacteria bound together by a slimy substance.
Through DNA analysis, Reith discovered that up to 30 species of bacteria were on the gold grains. The DNA sequence of one bacterium tagged it as a member of the species Ralstonia metallidurans, which happened to be the species most common on the gold grains. Further tests showed that these bacteria could actually precipitate gold out of a solution. To find out how exactly they were doing this, Reith examined the soils where the gold grains were found. The grains were embedded in soils located over gold-containing rocks.
Reith thinks that over time, moisture dissolves the gold inside the rocks. The gold the leaches upward into the soil where it comes into contact with the bacteria. The bacteria then build the grains up over a period of time.
In the laboratory, Reith placed a culture of the R. metallidurans in the presence of dissolved gold, which is typically toxic to most microorganisms. However, instead of dying, R. metallidurans showed “active gold precipitation.”
Current models of gold formation do not include a biological mechanism. This is why Reith’s discovery presents new opportunities for the “bioprocessing of gold ore.” It raises the possibility that bacteria might be used to process gold. In terms of exploration, biosensors could someday be used to detect the presence of bacteria, which, in turn, could lead prospectors to gold.
More abstracts about the Bug for Gold