By: Annie Cheung

Heavy metals ions, such as gold, are toxic to many species of bacteria. It is therefore surprising to see that the bacterium, Delftia acidovorans, can thrive on biofilms that form on top of gold deposits. Researchers at McMaster University have found a novel mechanism in which this gold-resistant bacterium is able to protect itself from this toxicity.

The research team led by Dr. Nathan Magarvey at Michael G. Degroote Institute for Infectious Disease Research has discovered that D. acidovorans is able to protect itself from toxic gold ions by excreting a metabolite, delftibactin, outside of its cell wall. Delftibactin is a small molecule compound that is able to precipitate soluble gold ions into nontoxic gold nanoparticles. This defense mechanism leads to the formation of a halo of gold platelets around D. acidovorans that resemble gold nuggets one would typically find in natural geological deposits. The conversion of toxic ions into harmless gold platelets prevents gold metal ions from entering D. acidovorans cells. “This finding is the first demonstration that a secreted metabolite can protect against toxic gold and cause gold biomineralization”, states Dr. Magarvey in his paper.

The discovery of delftibactin involved genome analysis to identify the gene responsible for this unique protection mechanism. Researchers grew a colony of D. acidovorans cells lacking the gene that codes for delftibactin A, the protein responsible for delftibactin synthesis. They found that the delftibactin-deficient bacteria struggled to survive in a medium supplied with toxic gold ions, while the addition of delftibactin A to the colony enabled the bacteria’s survival. Delftibactin A may potentially be used someday to identify gold-rich streams and rivers, or to precipitate gold from water.

The study did not specifically look into the viability of using the bacteria in gold-mining applications. Instead, Dr. Magarvey is more interested in understanding the chemical properties of the metabolite. In collaboration with Dr. Bin Ma at the University of Waterloo, Dr. Magarvey has recently developed a bioinformatics method that enables the discovery of elusive bioactive metabolites, such as delftibactin, in bacteria. Dr. Magarvey hopes to use this method to further understand the function of metabolites in bacteria found in humans and their possible applications in medicine.

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