Turning seawater into gold
Via a number of news sources, and published in Nature Chemical Biology: a report describing new research with a metallophore bacterium. Researchers at McMaster University in Ontario, Canada have been looking at microorganisms that have been associated with biofilms growing on gold nuggets. Gold, like many heavy metals, is toxic to many organisms. Consequently, it was surmised that any microorganisms that are able live in close proximity to these materials must have a mechanism for being able to survive by them. Sequencing of organisms in gold biofilms identified two species, Cupriavidus metallidurans and Delftia acidovorans that made up over 90% of the biofilm associated microbes. The researchers decided to focus on these two species in order to identify any potential mechanisms that they might have had to assure survival in the presence of lethal levels of soluble gold.
In order to do this, the full DNA sequences of the two microorganisms were compared, specifically to identify any small-molecule metabolites that might be produced in one of them but not the other that had previously been show to play a role in metal binding. They chose to examine D. acidovorans specifically, as that species was able to grow in significantly higher levels of soluble gold on a chemically defined medium, in comparison to C. metallidurans. DNA sequence analysis identified the delG gene from Delftia acidovorans that was present only that species. Molecular deletion of the delG gene in Delftia produced a bacterial strain unable to grow in the presence of soluble gold. The delG gene product was secreted from bacteria into the culture medium. The secreted material was named delftibactin, and was purified and further analyzed.
Purified delftibactin was found to precipitate gold from solution, and electron microscopy of the precipitated material showed the presence of octahedral gold nanoparticles which resembled the structures found in natural deposits. The authors suggest that biological activity by organisms such as Delftia might contribute to the formation of gold deposits, and that the delG gene enables these organisms to survive in environments that would ordinarily be toxic. If the interaction between delftibactin and soluble gold is specific, this might allow the organism to be used for the industrial purification of gold from very dilute sources. Seawater contains approximately 5 to 50 parts per thousand soluble gold. Scaling up production of delftibactin opens up the possibility that it might be used commercially to extract gold from this very rich source.
Bonus time, to promote additional Microbiology interactions: in the comment thread below, list an industrially important microorganism (scientific name), and the industrial process it is important for! Please note, no repeats allowed.