There's Gold in That Thar Periplasm
When thinking of a gold prospector, most of us conjure up a wizened old character leading a mule that carries his pick, gold pan, and rusty coffee pot. Nowadays, think of bacteria instead. Specifically, picture the bacterium Cupriavidus metallidurans (formerly Ralstonia metallidurans), which carries out the biomineralization of gold. It transforms toxic gold compounds into their metallic form via an active mechanism.
The leader of a large international research group working on this subject, Frank Reith of the University of Adelaide, explains: A number of years ago we discovered that the metal-resistant bacterium Cupriavidus metallidurans occurred on gold grains from two sites in Australia. The sites are 3500 km apart, in southern New South Wales and northern Queensland, so when we found the same organism on grains from both sites we thought we were onto something. 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 Au complexes leading to formation of gold biominerals.(Science News)
Transmission electron micrograph (TEM)
of a C. metallidurans ultra-thin section
containing a Au nanoparticle in the
periplasmic space. Source.
In a new study, they demonstrated that these organisms defend themselves against the oxidative stress induced by toxic Au(III) complexes by reducing the gold in them to particulate Au0. Using such fancy techniques as synchrotron µ-Xray fluorescence (µXRF), they localized a number of metals within the bacterial cells, something they could confirm with regular transmission EM. They also found that the genes involved are located in a new operon, and that they are upregulated when the bacteria are challenged with the toxic minerals. They suggest that this work may lead to the development of Au-specific biosensors. In other words, bacteria may be the gold prospectors of the future.
This is a revisit to this topic. For a previous post, click here.