McMaster University

McMaster University

Faculty of
Health Sciences

Scientists discover new small molecules that protect bacteria against toxic gold

Published: February 7, 2013
Nathan Magarvey
Nathan Magarvey, an assistant professor of biochemistry and biomedical sciences and chemistry & chemical biology
Diagram: nonribosomal peptides are necessary for Hemolysis
Shown is the gold-associated microbe, Delftia acidovorans, that is found to live in biofilms on gold nuggets. D. acidovorans produces a small molecule, delftibactin, that can complex toxic ionic gold and precipitate it to form non-toxic solid gold nano particles (the beginnings of a gold nugget). Shown on the right is D. acidovorans wild-type and on the left is a D. acidovorans mutant that can no longer produce delftibactin. The black halo around D. acidovorans wild-type is gold nano particles that are formed by delftibactin, effectively protecting D. acidovorans from toxic ionic gold.
[larger image]

McMaster researchers have discovered that gold resistant bacterium Delftia acidovorans can turn toxic water-soluble gold into a solid gold form, the first demonstration that gold-resistant microbe secretes a metabolite that can protect against toxic gold.

The research, published in Nature Chemical Biology, was led by Nathan Magarvey, an investigator with the Michael G. DeGroote Institute for Infectious Disease Research at McMaster University and assistant professor in the departments of biochemistry and biomedical sciences and chemistry & chemical biology.

"It has long been known that Delftia acidovorans live within gold nuggets, though how the bacteria avoid gold-mediated toxicity has been a mystery," Magarvey said. He added that he and colleagues (including collaborators at Western University) discovered that a molecule excreted out of the bacteria cells is capable of complexing gold ions and forming gold aggregates that are no longer toxic.

Magarvey and his team with Dr. Bin Ma (University of Waterloo) developed a bioinformatics method recently published in the Proceedings of the National Academy of Sciences. The tools they are building now leads them to finding elusive bioactive metabolites, and assisted in identifying the peptide-like delftibactin A small molecules.

Using this method, and biological activity assays, the team grew a colony of the bacterium Delftia acidovorans, and conducted tests to determine how it produces the molecular-sized gold nuggets outside its cell wall. They concluded the answer lies in a part of a molecule excreted by the microbe that both shields the organism and transforms the poisonous ions into particles.

"Our paper details a novel mechanism by which bacteria found on gold may protect themselves from toxic heavy metals, in this case gold," says graduate student Chad Johnston. "There is a protective mechanism by the gold resin bacteria in that it secretes a small molecule that binds it. What is interesting about this is the bacterium precipitates the molecule and forms gold nanoparticles and tiny gold platelets that are essentially the seeds of gold nuggets resembling those you would find in natural geological deposits. It is a novel mechanism for gold biomineralization, an extremely understudied but emerging field." This is likely one of several features that enable the bacterium to exist in such environments.

"The natural function of molecules is a very fascinating subject and sometimes you can relate that to the organism based on some environmental context," said Magarvey.

He hopes the finding will open doors to understanding the importance of natural small molecules in the environment and also within medicine. "Our focus is on how bacteria make molecules and the benefits that these molecules may have in medicine and in their ecological settings. Our next targets are those bugs that live on or within us, and realizing what roles human-associated bacteria and their metabolites play in our well-being and health."

Valid XHTML 1.0 Transitional Level Double-A conformance, W3C WAI Web Content Accessibility Guidelines 2.0