DEVELOPMENT OF A MICROBIAL PLATFORM FOR RARE EARTH LEACHING AND RECOVERY

Chemical methods for the extraction and refinement of technologically critical rare earth elements (REEs) are energy-intensive, hazardous, and environmentally destructive. Current biobased extraction systems rely on extremophilic organisms and generate many of the

same detrimental effects as chemical methodologies. The mesophilic methylotrophic bacterium Methylobacterium extorquens AM1 was previously shown to grow using electronic waste by naturally acquiring REEs to power methanol metabolism. We show that growth using electronic waste as a sole REE source is scalable up to 10 L with consistent metal yields and without harsh acids or high temperatures. The addition of organic acids increases REE leaching in a nonspecific manner. REE-specific bioleaching can be engineered through the overproduction of REE-binding ligands (called lanthanophores) and pyrroloquinoline quinone. REE bioaccumulation increases with the leachate concentration and is highly specific. REEs are stored intracellularly in polyphosphate granules, and genetic engineering to eliminate exopolyphosphatase activity increases metal accumulation, confirming the link between phosphate metabolism and biological REE use. We also show the ability of M. extorquens to grow using other complex REE sources, including pulverized smartphones and traditional mining ores, demonstrating the flexibility and potential for use as a recovery platform for these critical metals. Future work will focus on the development of the first rare earth element bacterial mining platform from primary and secondary materials.