Engineered strains enhance gold biorecovery from electronic scrap

• Engineered strains of C. violaceum carry additional cyanide producing operon.
• Engineered strains produced higher cyanide concentration than wild type.
• The pBAD strain showed the highest gold recovery of 30% at 0.5% w/v pulp density.
• As pulp density increased, the percentage of gold recovery generally decreased.

Gold bioleaching from electronic scrap materials (ESM) was examined using the bacterium Chromobacterium violaceum which produces and detoxifies cyanide, one of the few lixiviants capable of leaching gold. Gold recovery by the wild-type C. violaceum and two genetically engineered strains (pBAD and pTAC) with an additional cyanide-producing operon were investigated and compared. The ESM was pretreated to remove metals competing for metal cyanide complexation with gold. The effect of pulp density on leaching performance by the various strains was also investigated. The pBAD strain produced the highest cyanide concentration, and achieved the highest gold recovery of 30% at 0.5% w/v pulp density, compared to 11% recovery by the wild-type bacteria. Our results demonstrated the application of lixiviant metabolic engineering in the construction of enhanced bioleaching microbes for the bioleaching of precious metals from electronic waste.