A Canadian team of researchers has identified a molecule used by a bacterium to convert soluble gold ions into insoluble elemental gold.
Although soluble gold ions are inhibitory to most microorganisms, two species of bacteria are known to survive in their presence. The first, Cupriavidus metallidurans, has been studied for about a decade by researchers in Australia. More recently, a team led by Nathan Magarvey, who is cross-appointed to the departments of biochemistry and chemistry at McMaster University, decided to investigate the other organism, Delftia acidovorans. “We had a hunch that these bacteria might be using non-ribosomal peptides, which my lab studies frequently,” says Magarvey. Such biomolecules are used by other bacteria to bind iron and copper ions, so there was reason to suppose they might also exist for gold.
In a paper published in Nature Chemical Biology, the team exposed bacteria to gold ions; a dark halo of gold particles around the colonies indicated that de-solubilization was happening outside the cell. From these colonies they extracted a nonribosomal peptide they named delftibactin. Next, they used a computer algorithm to search through the D. acidovorans genome for sequences corresponding to enzymes that could make delftibactin. When these genes were removed, the haloes disappeared and the bacteria suffered. Adding the molecule back in by hand restored the dark haloes.
Due to the fact that it appears to create gold where none existed before, delftibactin has been dubbed the ‘Rumplestiltskin molecule’ in homage to the popular fairly tale character. Some speculate that it could be used to improve mining techniques. Magarvey shies away from the hype, but says his technique can be used to find other non-ribosomal peptides, including potential drugs. “These chemicals are produced by the bacteria inside us; as such they’re intrinsically bioactive,” he says.