Bacteria May Create Microbe-Assisted Gold Rush

Medieval alchemists may not have been able to turn other materials into gold, but a specific bacterium certainly can. The species forms nanoscale gold nuggets to help it grow in toxic solutions of the precious metal.

The findings, published in a paper in the online journal Nature Chemical Biology, examined bacteria which could one day be used to collect gold from mine waste.  For decades, biochemists have been aware that the bacterium, Cupriavidus metallidurans, finds gold metal to be toxic but at the same time, can isolate the metal inside its cells. However, there's another bacteria named Delftia acidovarans, which has also been found in the presence of biofilms on gold nuggets. In order to see if the bacteria could process the gold and extract it from the surrounding environment, Nathan Magarvey of McMaster University and his team conducted a series of tests.

The researchers grew D. acidovarans in the presence of a gold solution. They found that the bacterial colonies were actually surrounded by dark haloes of gold nanoparticles. As opposed to creating gold particles inside of its cells like C. metallidurans, it turned out that the other species of bacteria was actually creating gold particles outside its cell wall.

Using both genetically engineered and unengineered bacteria, the researchers then isolated the set of genes that work with a chemical metabolite that they named delftibactin. The combination of the genes and delftibactin was responsible for precipitating the gold. The scientists engineered some of the bacteria to lack the genes in order to test their theory, and found that the species no longer formed dark haloes. In addition, their growth was stunted in the presence of gold. The unengineered bacteria, in contrast, continued to produce gold and the chemical delftibactin.

The scientists theorize that by precipitating gold, D. acidovarans may be able to keep the metal from entering its cells in the solution. In addition, the genes they identified are probably involved in producing delftibactin and shunting it outside the cell.

These findings could pave the way for a veritable microbe-assisted gold rush. Since microscopic pieces of gold are often lost in the waste water associated with mining, this bacteria could potentially sort through the water and create enough gold to make the process a viable business venture. Until then, though, miners will have to keep panning for gold themselves.