Abstract
Biomining with acidophilic microorganisms has been used at commercial scale for the extraction of metals from various sulfide ores. With metal demand and energy prices on the rise and the concurrent decline in quality and availability of mineral resources, there is an increasing interest in applying biomining technology, in particular for leaching metals from low grade minerals and wastes. However, bioprocessing is often hampered by the presence of inhibitory compounds that originate from complex ores. Synthetic biology could provide tools to improve the tolerance of biomining microbes to various stress factors that are present in biomining environments, which would ultimately increase bioleaching efficiency. This paper reviews the state-of-the-art tools to genetically modify acidophilic biomining microorganisms and the limitations of these tools. The first part of this review discusses resilience pathways that can be engineered in acidophiles to enhance their robustness and tolerance in harsh environments that prevail in bioleaching. The second part of the paper reviews the efforts that have been carried out towards engineering robust microorganisms and developing metabolic modelling tools. Novel synthetic biology tools have the potential to transform the biomining industry and facilitate the extraction of value from ores and wastes that cannot be processed with existing biomining microorganisms.
Highlights
Biomining is a generic term used to describe the utilisation of microorganisms to process metal-containing ores and concentrates by bioleaching and biooxidation
The acid stress generated during biomining processes can be harmful to the growth of acidophiles, as demonstrated by the down-regulation of genes related to energy metabolism [65]
Synthetic and computational biology have the potential to improve the traits of naturally existing microorganisms so they can be productively implemented in biomining and other industrial processes
Summary
Biomining is a generic term used to describe the utilisation of microorganisms to process metal-containing ores and concentrates by bioleaching and biooxidation. After the undesirable sulfides are dissolved from the minerals, the gold or silver is typically leached with chemical lixiviants, such as cyanide Both bioleaching and biooxidation utilise similar acidophilic iron and/or sulfur-oxidising microorganisms to solubilise metal containing sulfides. In addition to the extraction of metals, bioreactors with acidophilic iron oxidising microorganisms can be utilised for the removal of excess iron, sulfate, and other contaminants from hydrometallurgical process waters and the generation/regeneration of biological reagents for use as lixiviants [7,8]. The impurities in low grade complex ores and the scarcity of freshwater in arid areas create challenges for the use of traditional biomining microorganisms as biomining microbes are typically sensitive to high ionic strength and elevated metal concentrations of saline leach liquors. This paper reviews resilience pathways that can be utilised to enhance the robustness and tolerance of microorganisms in harsh environments, and discusses the challenges and limitations of engineering such microbes for biomining applications
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