Group of Microbes Change Dissolved Gold to Solid

By John Roach
for National Geographic News

August 30, 2001

Breathing is a rich experience for a group of unusual microbes that typically live deep beneath the sea.

A microbiologist has found that microscopic organisms known as extremophiles breathe in dissolved gold and out comes the stuff of gold rings, necklaces, and earrings. The finding may explain how some gold ore deposits formed.

Ten years ago Derek Lovley, a microbiologist at the University of Massachusetts in Amherst, discovered that many microorganisms derive their energy by breathing in dissolved forms of toxic metals, such as uranium and cadmium, and converting them to solids.

"They use metals like we use oxygen," said Lovley. "It is the way they get energy."

Technology developed from that discovery is widely used today in pollution cleanup. Certain microbes are used to separate toxic metals from contaminated water and soil. The separated metal can then be scooped up and removed.

Electron Transfer

After the earlier finding, Lovley and his colleagues wondered if microorganisms that thrive in environments where dissolved gold is found, such as hydrothermal vents and hot springs, could convert dissolved gold to solid gold.

"We know they can reduce iron naturally and radioactive contaminants," he said. "What about gold? It has an oxide state and a reduced state."

In the laboratory, the researchers placed iron-reducing microbes in a gold solution similar to that found in a hydrothermal vent deep in the ocean. As they suspected, the microbes rapidly converted the gold from the dissolved form to a more valuable, insoluble metallic form.

The microbes do this by transferring electrons (negatively charged particles) to the dissolved metals. That process, in turn, removes the non-metallic elements—leaving behind solid deposits.

"When electrons are transferred onto the soluble gold it changes its state from ionic gold, Au+3, to metallic gold, which has no charge and is insoluble," said Lovley.

Gold Deposits

Continued on Next Page >>




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