Bacterium aids in formation of gold

ADELAIDE, Australia, Oct. 8 (UPI) -- An Australian-led team of international scientists says it's found the bacterium Cupriavidus metallidurans catalyses toxic gold compounds into metallic form.

Researchers previously reported the presence of bacteria on gold surfaces, but it was never determined what purpose they served.

In the new study, led by University of Adelaide research fellow Frank Reith, scientists have found there might be a biological reason for the presence of bacteria on gold grain surfaces.

"A number of years ago we discovered that the metal-resistant bacterium Cupriavidus metallidurans occurred on gold grains from two sites in Australia," Reith said. "The sites are (2,175 miles) apart in southern New South Wales and northern Queensland. So when we found the same organism on grains from both sites … it made us wonder why these organisms live in this particular environment.

"The results of this study point to their involvement in the active detoxification of (gold) complexes leading to formation of gold biominerals," he said.

Experiments showed C. metallidurans rapidly accumulates toxic gold complexes, promoting gold toxicity. That, researchers said, pushes the bacterium to induce oxidative stress and metal resistance clusters in order to defend its cellular integrity. That, in turn, leads to active biochemically-mediated reduction of gold complexes into nano-particulate, metallic gold, which might contribute to the growth of gold nuggets.

The study appears in the Proceedings of the National Academy of Sciences.