Conventional leaching (extraction) methods for gold recovery from electronic waste involve the use of strong acids and pose considerable threat to the environment. The alternative use of bioleaching microbes for gold recovery is non-pollutive and relies on the secretion of a lixiviant or (bio)chemical such as cyanide for extraction of gold from electronic waste. However, widespread industrial use of bioleaching microbes has been constrained by the limited cyanogenic capabilities of lixiviant-producing microorganisms such as Chromobacterium violaceum. Here we show the construction of a metabolically-engineered strain of Chromobacterium violaceum that produces more (70%) cyanide lixiviant and recovers more than twice as much gold from electronic waste compared to wild-type bacteria. Comparative proteome analyses suggested the possibility of further enhancement in cyanogenesis through subsequent metabolic engineering. Our results demonstrated the utility of lixiviant metabolic engineering in the construction of enhanced bioleaching microbes for the bioleaching of precious metals from electronic waste.
* These authors contributed equally to this work.
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he ever increasing demand for electronics, fueled by a rising affluence in societies, coupled with the short lifetime of electronic devices, has resulted in the generation of a torrential electronic waste stream in our modern world1. This electronic waste stream presents a major disposal challenge as electronic waste contains toxic metallics such as lead and mercury. In addition to its inherent toxicity, electronic waste also contains significant amounts of precious metals such as gold (Au). In fact, compared with natural Au ores, the Au content in electronic scrap material (ESM) is significantly higher (10 g to 10 kg Au per ton of ESM2,3 as compared to 0.5 g to 13.5 g Au per ton of natural Au ore3,4), creating an economic driving force for the recycling of electronic waste2,4. In 2009, the United Nations...