S95: Gold Biomineralization by a Novel Secondary Metabolite from a Gold-Associated Bacterium

Secondary metabolites are of significant industrial importance and are used by bacteria to enhance fitness, capture niches, and overcome environmental challenges including the maintenance of metal homeostasis. Metals represent an interesting environmental condition for microbes, as some are required for growth (e.g. Fe³⁺) while others inhibit it (e.g. Au³⁺, Ag⁺, Hg⁺). Gold nuggets are populated by a select number of bacteria; though soluble gold is inherently toxic, these bacteria are implicated in its accumulation and deposition. There is not yet a defined biochemical mechanism or logic associated with how bacteria biomineralize gold. Here we describe that the gold-associated bacterium Delftia acidovorans uses a secondary metabolite metallophore to alleviate Au³⁺ toxicity by forming gold particles that match those seen in natural deposits. We observed that D. acidovorans produces a characteristic darkening surrounding its colonies upon exposure to Au³⁺, and used genetic information to predict and isolate the secondary metabolite responsible for this activity – delftibactin. Though dispensable for growth, a genetically modified strain deficient in delftibactin synthesis shows a ~100 fold increase in susceptibility to ionic gold toxicity, which is effectively complemented by the addition of delftibactin. This secondary metabolite-mediated protection occurs through precipitation of Au³⁺, depositing it as insoluble solid gold and creating the natural substrate on which D. acidovorans can be found. Our results demonstrate that bacteria produce gold complexing small molecules, and these agents serve a novel function for secondary metabolites in remediating toxic environments, forming complex and valuable structures in the process.